A176815 Radius of the second-shortest interval (of positive length) centered at prime(n) that has prime endpoints, (zero if no solution exists).

0, 0, 0, 0, 8, 10, 12, 0, 18, 18, 28, 24, 18, 30, 24, 30, 30, 42, 30, 18, 30, 48, 30, 42, 54, 30, 24, 24, 42, 54, 30, 42, 36, 42, 42, 42, 54, 60, 60, 24, 48, 30, 60, 36, 60, 72, 18, 84, 36, 78, 36, 42, 42, 18, 24, 30, 42, 60, 36, 30, 84, 54, 30, 48, 84, 66, 48, 60, 54, 72, 36

Offset

1,5

Comments

7+-10->primes;but 7-10=-3,so,term #4(for number 7) is 0, 11+-8->primes, 13+-10->primes, 17+-12->primes, 19+-22->primes;but 19-22=-3,so,term #8(for number 19)is 0, 23+-18->primes,..

Links

Table of n, a(n) for n=1..71.

Mathematica

f[n_]:=Module[{a=1}, While[ !PrimeQ[n-a]||!PrimeQ[n+a], a++ ]; r[n, ++a]]; r[n_, k_]:=Module[{a=k}, While[ !PrimeQ[n-a]||!PrimeQ[n+a], a++ ]; If[a>n, 0, a]]; Table[f[Prime[n]], {n, 1, 5!}]

Crossrefs

Cf. A078611

Sequence in context: A062372 A046031 A102758 * A338473 A336143 A347267

Adjacent sequences: A176812 A176813 A176814 * A176816 A176817 A176818

Keyword

nonn

Author

Vladimir Joseph Stephan Orlovsky, Apr 26 2010

Status

approved