A139457 a(n)= smallest m such that primorial(n)/2 + 2^m is prime.

0, 1, 1, 1, 3, 1, 2, 4, 3, 1, 1, 1, 4, 10, 1, 11, 1, 2, 11, 14, 2, 8, 7, 3, 4, 4, 26, 21, 1, 4, 15, 10, 8, 4, 16, 29, 10, 3, 51, 17, 5, 12, 12, 48, 13, 45, 12, 1, 20, 17, 65, 12, 8, 95, 5, 12, 11, 8, 110, 38, 28, 8, 1, 23, 13, 5, 7, 11, 21, 2, 20, 32, 9, 66, 4, 2, 1, 20, 34, 97, 28, 80

Offset: 1

Author

Artur Jasinski, Apr 21 2008

Keywords

• nonn

Crossrefs

Cf. A067026, A067027, A139439-A139457, A103514.

Programs

Mathematica

k = 1/2; a = {}; Do[k = k*Prime[n]; m = 0; While[ ! PrimeQ[k + 2^m], m++ ]; Print[m]; AppendTo[a, m], {n, 100}]; a

PARI

a(n)=my(t=prod(i=2,n,prime(i)),m); while(!isprime(t+2^m), m++); m \\ Charles R Greathouse IV, Apr 28 2015

Extensions

a(1)=0 inserted and program corrected by Ray Chandler, Jun 16 2013