A115206 Least number d such that prime(n) -/+ 2d form a prime pair; prime(n) being the n-th prime.

1, 2, 3, 3, 3, 6, 3, 6, 6, 3, 6, 12, 3, 3, 6, 9, 3, 6, 3, 9, 12, 9, 15, 6, 3, 3, 15, 12, 12, 9, 15, 6, 9, 6, 3, 18, 15, 3, 6, 9, 21, 15, 15, 21, 6, 30, 15, 24, 3, 6, 15, 6, 3, 3, 6, 21, 3, 6, 27, 12, 12, 21, 18, 18, 9, 15, 18, 9, 3, 21, 15, 3, 15, 18, 15, 12, 9, 6, 15, 6, 6, 12, 9, 12, 9, 42, 9

Offset: 3

Author

Lekraj Beedassy, Mar 04 2006

Keywords

• nonn

Crossrefs

Cf. A078611.

Programs

Mathematica

f[n_] := Block[{k = 1, p = Prime@n}, While[ !PrimeQ[p - 2k] || !PrimeQ[p + 2k], k++ ]; k]; Table[f[n], {n, 3, 90}] (* Robert G. Wilson v, Mar 14 2006 *)

Formula

a(n) = A078611(n)/2.

Extensions

Corrected by N. J. A. Sloane, Mar 05 2006

More terms from Robert G. Wilson v, Mar 14 2006