A213512 Minimal of max(m,k) (m>=1,k>=0) such that (2*n-1)!!/m+2^k is prime.

1, 1, 1, 1, 1, 2, 3, 3, 2, 3, 1, 1, 3, 1, 2, 4, 5, 5, 5, 2, 3, 2, 4, 4, 7, 5, 4, 7, 1, 9, 6, 3, 6, 5, 13, 10, 2, 1, 7, 3, 6, 5, 5, 5, 9, 3, 2, 5, 9, 7, 11, 1, 3, 5, 10, 5, 7, 3, 3, 5, 9, 4, 5, 11, 8, 5, 9, 8, 11, 9, 9, 13, 9, 11, 11, 9, 5, 3, 11, 11, 3, 7, 3, 9, 1, 10, 7, 9, 3, 7, 7, 11, 9, 6, 9, 16, 5, 6, 9, 5, 9, 15, 11, 12, 3, 19, 7, 7, 3, 1, 19, 7, 9, 11, 4, 19, 5, 9, 7, 11, 13, 11, 1, 7, 15, 7, 15, 18, 11, 7, 5, 19, 15, 12, 7, 19, 14, 9, 7, 11, 3, 13, 10, 13, 16, 11, 9, 11, 7, 3

Offset

1,6

Links

Table of n, a(n) for n=1..150.

Prog

(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

Crossrefs

Cf. A212281, A212282, A212321, A212636, A212637, A212648, A213366.

Sequence in context: A130631 A282014 A241539 * A218774 A270824 A048198

Adjacent sequences: A213509 A213510 A213511 * A213513 A213514 A213515

Keyword

nonn

Author

Vladimir Shevelev, Feb 15 2013

Extensions

Terms beginning with a(6) were calculated by Peter J. C. Moses.

Status

approved