A179835 Smallest k > 0 such that prime(n-k) + prime(n+k) = 2*prime(n), or 0 if there is no such k.

0, 0, 1, 0, 2, 2, 2, 0, 0, 3, 3, 6, 3, 0, 0, 1, 7, 4, 8, 3, 0, 0, 7, 4, 6, 6, 2, 2, 0, 0, 6, 8, 7, 12, 0, 2, 1, 0, 6, 1, 2, 4, 8, 15, 15, 0, 1, 0, 0, 0, 6, 0, 0, 2, 1, 1, 0, 0, 6, 0, 0, 0, 19, 7, 0, 0, 17, 5, 29, 3, 15, 15, 5, 1, 5, 20, 20, 4, 7, 2, 21, 2, 21, 4, 3, 5, 4, 27, 3, 0, 0, 5, 28, 2, 0, 0, 0, 21, 0, 30

Offset: 1

Author

T. D. Noe, Jan 10 2011

Keywords

• nonn

Links

• T. D. Noe, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A178609 (largest k), A178670 (number of k)

Programs

Mathematica

nn=1000; p=Prime[Range[2*nn]]; Table[s=Take[p,n-1] + Reverse[Take[p, {n+1,2n-1}]]; pos=Position[s,2*p[[n]]]; If[pos=={}, 0, n-pos[[-1,1]]], {n, nn}]