A231120 Primes q of the form q = p^2 + 4 (p prime) such that r = q^2 + 4 and t = r^2 + 4 are also prime.

25877573, 124835933, 277455653, 2210598293, 2970577013, 34314969053, 43115615453, 90247970573, 93738231893, 116836126973, 153183783773, 720880808213, 1818659924933, 2068485397733, 2258777543933, 3449960763653, 3645300477293, 4501767897173, 4670625512573, 5238481845533, 6812794277693

Offset: 1

Author

Zak Seidov, Nov 04 2013

Keywords

• nonn

Comments

Positions of a(n) in A165218: 16, 29, 33, 74, 78, 105, 130, 333, 520, 547, 572, 716, 740, 820, 832, 865, 975.

The first primes such that t^2+4 is also prime are 93738231893, 2365771484804813, 4185535280578373, 4658429282719973, 7706774555568173, 7711174427503853, 25756066576859093.

Links

• Zak Seidov and Charles R Greathouse IV, Table of n, a(n) for n = 1..10000 (first 699 terms from Seidov)

Crossrefs

Subsequence of A165218.

Programs

PARI

forprime(p=2,1e7, if(isprime(q=p^2+4) && isprime(r=q^2+4) && isprime(r^2+4), print1(q", "))) \\ Charles R Greathouse IV, Nov 05 2013