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
Keywords
Examples
k=25: prime(25) + prime(26) = 97 + 101 = 198 = 2*3*3*11 and 11 < 25, so 25 is in this sequence;
Programs
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Mathematica
Select[Range[94], FactorInteger[Prime[#] + Prime[# + 1]][[-1, 1]] <= # &] (* Giovanni Resta, Jul 13 2018 *)
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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