This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A209868 #15 Mar 30 2012 17:23:15 %S A209868 0,0,0,0,2,0,20,56,114,248,106,1016,1992,4016,6506,7518,24496,50358, %T A209868 121610,261206,483160 %N A209868 a(n) = number of integers in range [2^(n-1),(2^n)-1] which permutation A209861/A209862 sends to even-sized orbits. %C A209868 a(0) gives the number of even-sized cycles in range [0,0], i.e. 0, as there is only one fixed point in that range. %e A209868 In range [2^(6-1),(2^6)-1] ([32,63]) of permutations A209861 & A209862, there are 6 cycles of size 1 (six fixed points), 2 cycles of size 3, one cycle of size 4, and 2 cycles of size 8, i.e. 6*1 + 2*3 + 1*4 + 2*8 = 32 in total, of which 4 + 2*8 elements are in even-sized cycles, thus a(6)=20. %Y A209868 a(n) = A000079(n-1) - A209867(n) for all n>0. Cf. A209860, A209863, A209864, A209865, A209866. %K A209868 nonn %O A209868 0,5 %A A209868 _Antti Karttunen_, Mar 24 2012