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

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, 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, 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

Offset: 2

Author

Vladimir Shevelev, Feb 15 2013

Keywords

• nonn

Crossrefs

Cf. A212281, A212282, A212321, A212636, A212637, A212648.

Programs

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

Extensions

Terms beginning with a(10) from Peter J. C. Moses