1/n! times the number of ordered pairs of permutation functions f,g on n elements where f(f(x)) = g(f(g(x))).

A255515

1/n! times the number of ordered pairs of permutation functions f,g on n elements where f(f(x)) = g(f(g(x))).

Terms

    a(0) =1a(1) =1a(2) =1a(3) =2a(4) =4a(5) =5a(6) =9a(7) =17a(8) =26a(9) =46a(10) =87a(11) =137a(12) =246a(13) =474a(14) =791a(15) =1420a(16) =2783a(17) =4839a(18) =8806a(19) =17361a(20) =31252a(21) =57613a(22) =114497a(23) =211496a(24) =395637a(25) =791597a(26) =1495016a(27) =2834242a(28) =5710510a(29) =10986325

External references