A174441 Primes p such that the concatenations p//1331 and 1331//p are both prime numbers (for naturals see A174355).

53, 347, 431, 641, 647, 821, 1709, 1973, 2081, 2591, 2657, 2963, 4073, 4139, 4643, 4787, 5039, 5483, 5657, 6029, 6791, 6917, 6959, 7127, 7673, 8273, 8693, 8807, 8849, 9221, 9311, 9689, 10139, 10457, 11423, 12503, 12743, 13619, 13913, 14549

Offset: 1

Author

Eva-Maria Zschorn (e-m.zschorn(AT)zaschendorf.km3.de), Mar 20 2010

Keywords

• base
• nonn

Comments

See comments and references for A173836, A174213.

Examples

			531331 = prime(43928), 133153 = prime(12427) => p(1) = 53 = prime(16).
3471331 = prime(248286), 1331347 = prime(102237) => p(2) = 347 = prime(69).
139131331 = prime(7865788), 133113913 = prime(7544750) => p(39) = 13913 = prime(1645).
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A168327, A168417, A173836, A174213, A174260, A174355.

Programs

Mathematica

Select[Prime[Range[2000]],AllTrue[{#*10^4+1331,1331*10^IntegerLength[ #]+#}, PrimeQ]&] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, May 08 2016 *)

PARI

isok(n) = isprime(n) && isprime(n*10^4 + 1331) && isprime(1331*10^(length(Str(n))) + n); \\ Michel Marcus, Aug 27 2013