A242773 -id:A242773 - cp's OEIS frontend

A242772 The lesser of twin primes p1 such that 2*p1 + p2 is a prime number (A174913) and also the lesser of other twin primes in A174913.

5, 11489, 32969, 33329, 33599, 42839, 58109, 93809, 96329, 114599, 180179, 272999, 309539, 334889, 401309, 540539, 633569, 717089, 784349, 820409, 870239, 879689, 907139, 948089, 989249, 991619, 994559, 1020959, 1028579, 1044749, 1185659, 1189649, 1245449, 1253909

Offset: 1

Ivan N. Ianakiev, May 22 2014

nonn

It seems that a(n) == 9 mod 10 for n > 1.

a(n) == 9 (mod 10) for n > 1 since if p1 == 1, 3 or 7 (mod 10) then 2*p1 + p2, p2, or 2*p1 + p2 + 2 is divisible by 5, respectively. - Amiram Eldar, Dec 31 2019

			a(1) = A174913(2) = 5 and 2*5 + 7 = 17 = A174913(3).

Amiram Eldar, Table of n, a(n) for n = 1..10000

Cf. A001359, A174913, A174920, A242773.

Select[Range[10^6], And @@ PrimeQ[{#, # + 2,(p = 3*# + 2), p + 2, 3*p + 2}] &] (* Amiram Eldar, Dec 31 2019 *)

isok(p) = isprime(p) && isprime(p+2) && isprime(q=3*p+2) && isprime(q+2) && isprime(3*q+2); \\ Michel Marcus, May 23 2014

cp's OEIS Frontend

A242772 The lesser of twin primes p1 such that 2*p1 + p2 is a prime number (A174913) and also the lesser of other twin primes in A174913.

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