A162110 - OEIS

A162110

Number of n X n symmetric binary arrays with rows, considered as graycode numbers, in strictly increasing order, and no more than 2 ones in any row or column

2, 4, 8, 21, 53, 145, 405, 1180, 3562, 11030, 35306, 115338, 387443, 1326992, 4650201, 16604351, 60443887, 223971602, 844095896, 3234044019, 12582749734, 49703821584, 199149007691, 809153896365, 3331563584486