A038780 An intermediate sequence for counting nonisomorphic circulant directed p^2-graphs, indexed by odd primes p.

9, 36, 196, 11664, 123904, 16941456, 213218404, 36384036516, 91921690256400, 1281107924034624, 3643830108147610000, 755580082985683928064, 10965324181121364597904, 2340151860941299402849476, 7500891349210337560308603456, 24695823438181435496869784039184

Offset

1,1

Links

Table of n, a(n) for n=1..16.

M. Klin, V. A. Liskovets and R. Poeschel, Analytical enumeration of circulant graphs with prime-squared vertices, Sem. Lotharingien de Combin., B36d, 1996, 36 pages.

Formula

a(n) = A049297(prime(n+1))^2.

a(n) = ( (1/(p-1)) * Sum_{r|p-1} phi(r) * 2^((p-1)/r) )^2 where p = prime(n+1). - Sean A. Irvine, Feb 14 2021

Prog

(PARI) a(n) = my(p=prime(n+1)); (((1/(p-1)) * sumdiv(p-1, r, eulerphi(r) * 2^((p-1)/r)))^2); \\ Sean A. Irvine, Feb 14 2021

Crossrefs

Cf. A038777, A038779.

Sequence in context: A280353 A110752 A094973 * A073984 A036907 A027381

Adjacent sequences: A038777 A038778 A038779 * A038781 A038782 A038783

Keyword

nonn,easy

Author

N. J. A. Sloane, May 04 2000

Extensions

More terms from Valery A. Liskovets, May 09 2001

More terms from Sean A. Irvine, Feb 14 2021

Status

approved