Irregular triangle read by rows: T(n,k) = number of size k subsets of S_n that remain unchanged by a rotation of 90 degrees.

A277085

Irregular triangle read by rows: T(n,k) = number of size k subsets of S_n that remain unchanged by a rotation of 90 degrees.

Terms

    a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =0a(6) =1a(7) =1a(8) =0a(9) =1a(10) =0a(11) =1a(12) =0a(13) =1a(14) =1a(15) =2a(16) =4a(17) =6a(18) =10a(19) =14a(20) =20a(21) =26a(22) =31a(23) =36a(24) =40a(25) =44a(26) =44a(27) =44a(28) =40a(29) =36

External references