A071218 Numbers k such that the largest prime factor of the sum of the two consecutive primes prime(k) + prime(k+1) is at most k.

2, 3, 4, 5, 6, 7, 8, 10, 13, 14, 15, 16, 17, 18, 20, 21, 22, 25, 26, 27, 28, 30, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 52, 53, 55, 56, 57, 59, 60, 61, 62, 64, 65, 66, 68, 69, 70, 72, 73, 74, 78, 79, 80, 81, 82, 83, 85, 88, 89, 90, 91, 92, 94

Offset: 1

Author

Labos Elemer, May 17 2002

Keywords

• nonn

Examples

			k=25: prime(25) + prime(26) = 97 + 101 = 198 = 2*3*3*11 and 11 < 25, so 25 is in this sequence;
		

Crossrefs

Cf. A006530, A001043, A071216, A071217, A071219.

Programs

Mathematica

Select[Range[94], FactorInteger[Prime[#] + Prime[# + 1]][[-1, 1]] <= # &] (* Giovanni Resta, Jul 13 2018 *)

PARI

isok(n) = vecmax(factor(prime(n)+prime(n+1))[,1]) <= n; \\ Michel Marcus, Jul 09 2018

Formula

If A071216(k) <= k, then k is in this sequence.

Extensions

Edited by Jon E. Schoenfield, Jul 08 2018