cp's OEIS Frontend

A213366 Minimal of max(m,k) (m>=1,k>=0) such that (2*n-1)!!/m-2^k is prime.

%I A213366 #59 Nov 16 2014 06:54:19
%S A213366 1,1,1,2,2,2,1,1,1,5,3,2,6,5,3,5,2,3,3,3,3,5,5,3,1,7,5,8,7,3,5,5,5,5,
%T A213366 7,1,9,7,2,2,3,3,7,1,3,10,7,5,4,11,9,2,9,7,9,9,13,13,9,3,9,5,12,7,1,5,
%U A213366 7,5,9,6,3,5,5,11,10,1,5,5,7,3,3,3,8,9,2,6,7,4,7,9,5,4,6,7,5,10,15,4,9,11,15,9,21,13,7,11,7,8,7,8,12,7,4,12,5,7,20,9,5,21,2,1,3,9,5,13,16,13,9,4,15,11,13,5,2,9,7,11,11,11,17,9,8,9,15,15,2,12,3
%N A213366 Minimal of max(m,k) (m>=1,k>=0) such that (2*n-1)!!/m-2^k is prime.
%o A213366 (PARI) a(n)=my(m=-1, P=prod(i=2, n, 2*i-1)); while(m+=2, for(k=m-2, m-1, forstep(M=1, m-2, 2, if(ispseudoprime(P/M-2^k), return(k)))); for(k=0, m, if(ispseudoprime(P/m-2^k), return(m)))) \\ _Charles R Greathouse IV_, Feb 27 2013
%Y A213366 Cf. A212281, A212282, A212321, A212636, A212637, A212648.
%K A213366 nonn
%O A213366 2,4
%A A213366 _Vladimir Shevelev_, Feb 15 2013
%E A213366 Terms beginning with a(10) from _Peter J. C. Moses_