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A051636 Number of "labeled" cyclic subgroups of alternating group A_n. 3
1, 1, 2, 8, 32, 167, 947, 6974, 53426, 454682, 4303532, 50366912, 553031624, 6760260236, 90333982832, 1369522152392, 20986020606632, 350528387240264, 5751957395258096, 111685506968916032, 2139383543480892032 (list; graph; refs; listen; history; internal format)
OFFSET

1,3

FORMULA

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.

CROSSREFS

Cf. A051625.

Sequence in context: A030872 A030835 A137975 * A081561 A009753 A141202

Adjacent sequences:  A051633 A051634 A051635 * A051637 A051638 A051639

KEYWORD

easy,nonn

AUTHOR

Vladeta Jovovic (vladeta(AT)eunet.rs)

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Last modified February 14 11:36 EST 2012. Contains 205623 sequences.