31018

Appears in sequences

• Number of lower triangular n X n arrays colored with integers 0 upwards introduced in row major order, with no element equal to any element at a city block distance of two, and containing the value n(n+1)/2-2.at n=21A212031
• Number of inequivalent ways of placing 2 nonattacking rooks on n X n board up to rotations and reflections of the board.at n=26A307304
• a(n) = A115004(n) - A334701(n).at n=25A335179