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Theme: Primes Inside, Outside, and with a Square

Author/Opus: This is the 9th puzzle from guest contributor Joseph Howard.

Rules: Fill each cell with a digit from 1 to 9 (1 to 6 in example) so that no digit repeats in any row or column, and also draw a single, non-intersecting loop through some of the cells in the grid. The loop cannot pass through gray cells. Numbers on the outside of the grid show the sum of digits of ALL horizontal/vertical loop segments in that row/column in order. (Note: as in column 5 of the example, only segments that pass horizontally/vertically in a row/column appear as clues; the 5 in that column is not part of a vertical segment and is not represented by a clue). Not all outside clues are given, and unclued rows/columns can have any possible distribution of loop segments/sums.

Answer String: Enter the digits in the 3rd row from left to right, followed by a comma, followed by the 9th row from left to right.

Time Standards (highlight to view): Grandmaster = 20:00, Master = 30:00, Expert = 1:00:00

Note: Follow this link for other less common Number Placement puzzles.