1,3

a(n) = 1/2*Sum_{pi} (1+(-1)^(k_2+k_4+...)) * n!/(k_1!*1^k_1*k_2!*2^k_2*...*k_n!*n^k_n*phi(lcm{i:k_i != 0})), where pi runs through all partitions k_1+2*k_2+...+n*k_n=n and phi is Euler's function.

Cf. A051625.

Sequence in context: A030872 A030835 A137975 this_sequence A081561 A009753 A141202

Adjacent sequences: A051633 A051634 A051635 this_sequence A051637 A051638 A051639

easy,nonn

Vladeta Jovovic (vladeta(AT)eunet.rs)