%I #17 Dec 14 2019 21:28:04
%S 0,0,3,26,50,133,196,375,806,1001,1768,2451,2850,3773,5500,7686,8526,
%T 11408,13651,14875,18981,22100,27391,35673,40376,42875,48178,50986,
%U 56925,81313,89376,102443,107066,132276,137751,155078,173800,187083,208250,230956,238876,281201
%N a(n) is the genus of the modular curve associated to the principal congruence subgroup of level p(n), where p(n) is the n-th prime number.
%H Jens Putzka, <a href="http://www.jens.putzka.net/download/diplomarbeit.pdf">Aequivariante Signaturen und Darstellungen der Modulgruppe in der Kohomologie von Modulkurven</a>, Master's Thesis (2006), page 18.
%F a(n) = (prime(n)+2)*(prime(n)-3)*(prime(n)-5)/24.
%o (PARI) a(p)=(p+2)*(p-3)*(p-5)/24;
%o forprime(p=3,1000,print1(a(p),", "));
%K nonn,easy
%O 2,3
%A _Gaël Collinet_, Jun 08 2011