A221951 - OEIS

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A221951

Number of subgroups of C_4 X C_n.

3, 8, 6, 15, 6, 16, 6, 22, 9, 16, 6, 30, 6, 16, 12, 29, 6, 24, 6, 30, 12, 16, 6, 44, 9, 16, 12, 30, 6, 32, 6, 36, 12, 16, 12, 45, 6, 16, 12, 44, 6, 32, 6, 30, 18, 16, 6, 58, 9, 24, 12, 30, 6, 32, 12, 44, 12, 16, 6, 60, 6, 16, 18, 43, 12, 32, 6, 30, 12, 32, 6, 66, 6, 16, 18, 30, 12, 32, 6, 58

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OFFSET

1,1

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..65537

FORMULA

a(n) = Sum_{d|n} (1+gcd(2,d)+gcd(4,d)). - Antti Karttunen, Sep 30 2018

PROG

(PARI) A221951(n) = sumdiv(n, d, (1+gcd(2, d)+gcd(4, d))); \\ Antti Karttunen, Sep 30 2018

CROSSREFS

Row 4 of A216624.

Cf. A000005, A069735.