A187561 Least number k >= 0 such that prime(n)*(prime(n)-k)-1 is prime.

0, 1, 1, 1, 1, 5, 1, 7, 7, 1, 1, 7, 11, 13, 1, 5, 7, 1, 1, 1, 7, 23, 5, 7, 1, 1, 5, 11, 7, 5, 1, 1, 13, 1, 1, 11, 7, 29, 13, 5, 11, 1, 13, 7, 1, 13, 13, 13, 7, 11, 25, 13, 1, 17, 5, 5, 1, 11, 11, 11, 17, 13, 1, 7, 17, 7, 1, 17, 5, 37, 25, 1, 11, 25, 1, 5, 43, 1, 37, 1

Offset

1,6

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Mathematica

Table[k = 0; While[! PrimeQ[Prime[n]*(Prime[n] - k) - 1], k++]; k, {n, 100}]

Prog

(PARI) a(n)=my(p=prime(n)); for(k=0, p, if(isprime(p*(p-k)-1), return(k))) \\ Charles R Greathouse IV, Jul 26 2011

Crossrefs

Sequence in context: A035109 A301509 A101263 * A088515 A200638 A322104

Adjacent sequences: A187558 A187559 A187560 * A187562 A187563 A187564

Keyword

nonn

Author

Pierre CAMI, Mar 13 2011

Status

approved