A241945 Indices n where both prime(n) + 2*prime(n+1) and 2*prime(n) + prime(n+1) are primes.
2, 3, 6, 17, 27, 30, 48, 53, 57, 68, 94, 137, 138, 143, 156, 157, 248, 259, 269, 289, 296, 316, 360, 369, 402, 425, 429, 430, 432, 446, 474, 500, 522, 580, 596, 631, 656, 760, 777, 810, 828, 875, 906, 951, 994, 1154, 1163, 1233, 1273, 1338, 1346, 1352, 1378, 1381, 1385, 1391, 1402, 1422, 1436, 1495, 1552, 1602
Offset: 1
Keywords
Examples
n=2 is in the sequence because 3 + 2*5 = 13 and 5 + 2*3 = 11 are primes. n=3 is in the sequence because 5 + 2*7 = 19 and 7 + 2*5 = 17 are primes. n=6 is in the sequence because 17 + 2*13 = 43 and 13 + 2*17 = 47 are primes.
Links
- Amiram Eldar and Zak Seidov, Table of n, a(n) for n = 1..10000
Crossrefs
Programs
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PARI
isok(n) = my(p=prime(n), q=nextprime(p+1)); isprime(p+2*q) && isprime(2*p+q); \\ Michel Marcus, Jan 06 2019