A038780 - OEIS

%I #23 May 02 2024 14:44:02

%S 9,36,196,11664,123904,16941456,213218404,36384036516,91921690256400,

%T 1281107924034624,3643830108147610000,755580082985683928064,

%U 10965324181121364597904,2340151860941299402849476,7500891349210337560308603456,24695823438181435496869784039184

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

%H M. Klin, V. A. Liskovets and R. Poeschel, <a href="http://www.mat.univie.ac.at/~slc/wpapers/s36klp.html">Analytical enumeration of circulant graphs with prime-squared vertices</a>, Sem. Lotharingien de Combin., B36d, 1996, 36 pages.

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

%F 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

%o (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

%Y Cf. A038777, A038779.

%K nonn,easy

%O 1,1

%A _N. J. A. Sloane_, May 04 2000

%E More terms from _Valery A. Liskovets_, May 09 2001

%E More terms from _Sean A. Irvine_, Feb 14 2021