0,1

a(3)=3 and a(5)=15 are the only odd numbers in this sequence.

P. Erdos, solved by J. Fiedler, Elem. Math. 16 (1961), 42-44, Aufgabe 374.

a(n)=2*A000142(n)/A027423(n).

a(4)=2*4!/d(4!)=2*24/8=6.

Cf. A000142, A027423.

Sequence in context: A147851 A143596 A091712 this_sequence A049798 A165198 A024682

Adjacent sequences: A125718 A125719 A125720 this_sequence A125722 A125723 A125724

nonn

Franz Vrabec (franz.vrabec(AT)aon.at), Feb 01 2007