147

Fill the grid with the digits 1-7 so that each digit appears once in each row and column.

147: A digit in column 1 indexes the position of the digit 1 in its row. (eg if r3c1 is a 6, then r3c6 is a 1.) A digit in column 4 indexes the position of the digit 4 in its row. A digit in column 7 indexes the position of the digit 7 in its row.

DOUBLES: There is exactly one doubler cell in each row and column, with each digit from 1-7 appearing once on a doubler. The value of a digit in a doubler cell is double its face value, for the purposes of the kropki ball and black line rules below.

KROPKI BALLS: The score on a coloured ball indicates the difference between the values of the two cells it sits between.

BLACK LINES: Values of adjacent cells along the black lines have a difference of at least 4 (Dutch Whisper).