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

Author

Vladimir Joseph Stephan Orlovsky, Apr 26 2010

Keywords

• nonn

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,..

Crossrefs

Cf. A078611

Programs

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!}]