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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. 1

%I #15 Jul 15 2018 12:22:37

%S 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 36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,52,53,55,56,57,59,60,61,

%U 62,64,65,66,68,69,70,72,73,74,78,79,80,81,82,83,85,88,89,90,91,92,94

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

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

%t Select[Range[94], FactorInteger[Prime[#] + Prime[# + 1]][[-1, 1]] <= # &] (* _Giovanni Resta_, Jul 13 2018 *)

%o (PARI) isok(n) = vecmax(factor(prime(n)+prime(n+1))[,1]) <= n; \\ _Michel Marcus_, Jul 09 2018

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

%K nonn

%O 1,1

%A _Labos Elemer_, May 17 2002

%E Edited by _Jon E. Schoenfield_, Jul 08 2018

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