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Theme: Tau Cross

Author/Opus: This is the 79th puzzle from our contributing puzzlemaster John Bulten.

Rules: Standard Sudoku rules. Also, standard Skyscrapers rules.

Difficulty: 4.5 stars

Time Standards (highlight to view): Grandmaster = 8:00, Master = 14:00, Expert = 28:00

Solution: PDF; a solution video is also available here.

Note: Follow this link for classic Skyscrapers puzzles and this link for variations on Skyscrapers puzzles. If you are new to this puzzle type, here are our easiest Skyscrapers Puzzles to get started on. More Skyscrapers puzzles can be found in The Art of Puzzles, in our beginner-friendly collection Intro to GMPuzzles by Serkan Yürekli, and in the e-book Skyscrapers by Ashish Kumar.

This year, we have started to have some extra difficult Sunday Stumpers, about once a month. These will be quite tough puzzles, but with a logical path to be found (and solution videos to help). This second Sunday Stumper is a challenging Sudoku variation with a special theme for Pi Day, whether you like Pi or are in the Anti-Pi = Tau camp.

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Theme: Pinenut

Author/Opus: This is the 320th puzzle from our managing editor Serkan Yürekli.

Rules: Standard Sudoku rules. Also, no two of 3, 1, and 4 can appear in adjacent cells. Some cages are marked by dashed lines; the sum of the digits in each cage must equal the value given in the upper-left corner of that cage (digits cannot repeat inside a cage). Some arrows given outside the grid indicate the sum of the digits along that diagonal path (digits can repeat on a diagonal). The value of any ungiven sum in either a cage or an arrow must not be a number composed solely of the digits 3, 1, and 4 (like 4, 11, 14, 31).

Difficulty: 5 stars

Time Standards (highlight to view): Grandmaster = 28:00, Master = 1:00:00, Expert = 2:00:00

Solution: PDF; a solution video is also available here from Dr. Sudoku and another video here from Cracking the Cryptic.

Note: Follow this link for other variations on Sudoku.

This year, we are going to have some extra difficult Sunday Stumpers, about once a month. These will be quite tough puzzles, but with a logical path to be found (and solution videos to help). This first Sunday Stumper is a challenging Sudoku variation in the style of some of the unusual rule mash-ups and difficulty seen on the Cracking the Cryptic channel.

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Theme: Have a Cracking New Year!

Author/Opus: This is the 371st puzzle from Thomas Snyder, aka Dr. Sudoku.

Rules: Standard Sudoku rules. Some arrow shapes are in the grid; the sum of the digits along the path of each arrow must equal the digit in the circled cell (digits can repeat on an arrow). Some thermometer shapes are in the grid; the digits along the thermometer must be strictly increasing from the round bulb to the flat end. Some rectangular cages are in the grid marked by dashed lines; the sum or product of the digits in these cages must be either 20 or 21. Finally, some arrows are given outside the grid; the sum or product of the digits along these marked diagonals must be either 20 or 21 (digits can repeat on a diagonal).

Difficulty: 5 stars

Time Standards (highlight to view): Grandmaster = 15:00, Master = 30:00, Expert = 60:00

Solution: PDF; a solution video from Cracking the Cryptic is here.

Note: Follow this link for other variations on Sudoku.

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Theme: XV

Author/Opus: This is the 56th puzzle from our contributing puzzlemaster Ashish Kumar.

Rules: Standard Sudoku rules. Also, whenever the numbers in two adjacent cells sum to exactly 10 or 5, an X or V is placed on the edge between cells reflecting the Roman numerals for 10 or 5. All adjacent cells not marked with an X or V cannot add up to 10 or 5.

Difficulty: 3.5 stars

Time Standards (highlight to view): Grandmaster = 4:00, Master = 7:00, Expert = 14:00

Solution: PDF; a solution video is also available here.

Note: Follow this link for other variations of Sudoku and this link for classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on.

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Theme: RHYTHM HEAVEN

Author/Opus: This is the 325th puzzle from our contributing puzzlemaster Grant Fikes.

Rules: Variation of Sudoku rules. Instead of the digits 1-9, use the letters in “RYTM HEAVN”

Difficulty: 3 stars

Time Standards (highlight to view): Grandmaster = 4:30, Master = 6:15, Expert = 12:30

Solution: PDF

Note: Follow this link for other classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on. More classic Sudoku puzzles can be found in The Art of Sudoku, The Art of Sudoku 2 and in our beginner-friendly collection Intro to GMPuzzles by Serkan Yürekli.

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Theme: Empty Inside

Author/Opus: This is the 179th puzzle from our contributing puzzlemaster Prasanna Seshadri.

Rules: Standard Sudoku rules. Additionally, the numbers outside the grid indicate the sum of the first N cells in that row/column from that direction, for some value of N from 1 to 9.

Answer String: Enter the 8th row from left to right, followed by a comma, followed by the 5th column from top to bottom.

Time Standards (highlight to view): Grandmaster = 12:00, Master = 18:00, Expert = 36:00

Solution: PDF

Note: Follow this link for other variations of Sudoku and this link for classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on.

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or solve online (using our beta test of Penpa-Edit tools; use tab to alternate between Sudoku number entry mode and a line mode to mark the snake.)

Theme: Clue Symmetry and Logic

Author/Opus: This is the 279th puzzle from our contributing puzzlemaster Serkan Yürekli.

Rules: Standard Sudoku rules. Additionally, locate a snake (a 1-cell wide path) that connects the gray circles marked with 1 and 9. The snake cannot touch itself, even diagonally. All cells marked with white circles must be part of the snake. Along the path, the snake must pass straight through any cell with an odd number from the sudoku, and must make a 90-degree turn in any cell with an even number from the sudoku.

Answer String: Enter the 2nd row from left to right, followed by a comma, followed by the 5th row from left to right.

Time Standards (highlight to view): Grandmaster = 5:15, Master = 9:00, Expert = 18:00

Solution: PDF

Note: Follow this link for other variations of Sudoku and this link for classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on.

(Note: This bonus puzzle is being posted today to mark the occasion of Prasanna’s birthday.)

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Theme: 28 from 03/02 1991-2019

Author/Opus: This is the 173rd puzzle from our contributing puzzlemaster Prasanna Seshadri.

Rules: Standard Sudoku rules. The numbers outside the grid indicate the sum of all digits between the 8 and the 9 in that row or column. Also, as in Consecutive Pairs Sudoku, if a gray circle is given between two adjacent cells, then the two numbers in those cells must be consecutive. (Note: not all gray circles are given; adjacent cells without a circle may contain either consecutive numbers or nonconsecutive numbers.)

Answer String: Enter the 1st row from left to right, followed by a comma, followed by the 7th row from left to right.

Time Standards (highlight to view): Grandmaster = 6:45, Master = 10:00, Expert = 20:00

Solution: PDF

Note: Follow this link for other variations of Sudoku and this link for classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on.

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Theme: Feng Shui (Clue symmetry, and 7 of the regions have one line of symmetry for the region and for the clues)

Author/Opus: This is the 12th puzzle from guest contributor Bryce Herdt.

Rules: Insert a letter from FENG SHUI into each cell so that no letter repeats in any row, column, or bold region.

Answer String: Enter the 4th row from left to right, followed by a comma, followed by the 8th row from left to right. Use CAPITAL LETTERS.

Time Standards (highlight to view): Grandmaster = 2:45, Master = 4:45, Expert = 9:30

Solution: PDF

Note: Follow this link for other variations of Sudoku and this link for classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on.

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Theme: Clue Symmetry and Logic

Author/Opus: This is the 10th puzzle from guest contributor Ashish Kumar.

Rules: Standard Sudoku rules. Also, whenever the numbers in two adjacent cells sum to exactly 10 or 5, an X or V is placed on the edge between cells reflecting the Roman numerals for 10 or 5. All adjacent cells not marked with an X or V cannot add up to 10 or 5.

Answer String: Enter the 6th row from left to right, followed by a comma, followed by the 9th row from left to right.

Time Standards (highlight to view): Grandmaster = 8:30, Master = 15:00, Expert = 30:00

Solution: PDF

Note: Follow this link for other variations of Sudoku and this link for classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on.