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

1,5

Links

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

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}]

Prog

(PARI) a(n)= my(q=prime(n), q2=q*2, p=q, k=0); forprime(r=q+1, q2-1, k++; if((p=precprime(p-1))+r == q2, return(k))); 0; \\ Ruud H.G. van Tol, Jun 03 2026

Crossrefs

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

Sequence in context: A212438 A112790 A329922 * A110857 A108867 A218604

Adjacent sequences: A179832 A179833 A179834 * A179836 A179837 A179838

Keyword

nonn,easy,look

Author

T. D. Noe, Jan 10 2011

Status

approved