A023313 Primes that remain prime through 4 iterations of function f(x) = 5x + 2.

373, 1171, 13687, 21997, 25657, 61603, 74413, 76471, 84199, 87181, 93487, 114691, 135859, 170761, 174877, 184333, 192979, 196177, 207931, 209743, 244219, 276229, 286687, 292561, 297811, 334603, 338893, 405037, 408361, 417097, 439141, 446323

Offset: 1

Author

David W. Wilson

Keywords

• nonn

Comments

Primes p such that 5*p+2, 25*p+12, 125*p+62 and 625*p+312 are also primes. - Vincenzo Librandi, Aug 04 2010

Numbers k such that A280720(k) > 3. - Felix Fröhlich, Jan 07 2017

Links

• John Cerkan, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A280720. Subsequence of A023217, A023252, A023283, and A111223.

Programs

Magma

[n: n in [1..1000000] | IsPrime(n) and IsPrime(5*n+2) and IsPrime(25*n+12) and IsPrime(125*n+62) and IsPrime(625*n+312)]; // Vincenzo Librandi, Aug 04 2010

Mathematica

Select[Range[10^6], Times @@ Boole@ Map[PrimeQ, NestList[5 # + 2 &, #, 4]] == 1 &] (* Michael De Vlieger, Jan 09 2017 *)

Formula

a(n) == 31 or 37 (mod 42). - John Cerkan, Oct 07 2016