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A038780 An intermediate sequence for counting nonisomorphic circulant directed p^2-graphs, indexed by odd primes p. 2
9, 36, 196, 11664, 123904, 16941456, 213218404, 36384036516, 91921690256400, 1281107924034624, 3643830108147610000, 755580082985683928064, 10965324181121364597904, 2340151860941299402849476, 7500891349210337560308603456, 24695823438181435496869784039184 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
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
Sequence in context: A280353 A110752 A094973 * A073984 A036907 A027381
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

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Last modified March 19 06:05 EDT 2024. Contains 370952 sequences. (Running on oeis4.)