cp's OEIS Frontend

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.

%I A071218 #15 Jul 15 2018 12:22:37
%S A071218 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,
%T A071218 36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,52,53,55,56,57,59,60,61,
%U A071218 62,64,65,66,68,69,70,72,73,74,78,79,80,81,82,83,85,88,89,90,91,92,94
%N 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.
%F A071218 If A071216(k) <= k, then k is in this sequence.
%e A071218 k=25: prime(25) + prime(26) = 97 + 101 = 198 = 2*3*3*11 and 11 < 25, so 25 is in this sequence;
%t A071218 Select[Range[94], FactorInteger[Prime[#] + Prime[# + 1]][[-1, 1]] <= # &] (* _Giovanni Resta_, Jul 13 2018 *)
%o A071218 (PARI) isok(n) = vecmax(factor(prime(n)+prime(n+1))[,1]) <= n; \\ _Michel Marcus_, Jul 09 2018
%Y A071218 Cf. A006530, A001043, A071216, A071217, A071219.
%K A071218 nonn
%O A071218 1,1
%A A071218 _Labos Elemer_, May 17 2002
%E A071218 Edited by _Jon E. Schoenfield_, Jul 08 2018