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

%I #16 Dec 31 2019 08:21:09

%S 7,11491,32971,33331,33601,42841,58111,93811,96331,114601,180181,

%T 273001,309541,334891,401311,540541,633571,717091,784351,820411,

%U 870241,879691,907141,948091,989251,991621,994561,1020961,1028581,1044751,1185661,1189651,1245451,1253911

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

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

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

%H Amiram Eldar, <a href="/A242773/b242773.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A242772(n) + 2.

%e a(1) = 7, 7 - 2 = 5 = A174913(1) and 2*A174913(1) + 7 = A174913(2).

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

%Y Cf. A001359, A174913, A242772.

%K nonn

%O 1,1

%A _Ivan N. Ianakiev_, May 22 2014