1,3

See A163951 for the cases ending with length 2 cycles and fixed points.

Any period 3 permutation (or disjoint combinations) is one element to be counted. This starts with n=3, where there are only 2 cases:

f1:{1,2,3}->{2,3,1} and f2:{1,2,3}->{3,1,2}

but for n>3 there are other elements (non permutations) to be counted

(for instance, with n=5, we count with f:{1,2,3,4,5}->{2,4,5,3,4}).

Cf. A163951, A163947, A163859.

Sequence in context: A127697 A109772 A115418 this_sequence A022028 A013776 A022019

Adjacent sequences: A163949 A163950 A163951 this_sequence A163953 A163954 A163955

more,nonn

Carlos Alves (cjsalves(AT)gmail.com), Aug 07 2009