A174355 Natural numbers n such that the concatenations n//1331 and 1331//n are prime numbers.

53, 57, 153, 249, 279, 329, 333, 339, 347, 381, 399, 431, 471, 489, 641, 647, 711, 821, 851, 923, 959, 987, 1169, 1239, 1313, 1383, 1479, 1547, 1563, 1589, 1611, 1653, 1677, 1709, 1773, 1863, 1887, 1973, 2031, 2067

Offset: 1

Author

Eva-Maria Zschorn (e-m.zschorn(AT)zaschendorf.km3.de), Mar 17 2010

Keywords

• base
• nonn

Comments

See comments and references for A173836, A174213.

Intersection of A173579 and A174213. - Michel Marcus, Aug 27 2013

Examples

			531331 = prime(43928), 133153 = prime(12427), 53 is smallest term of sequence.
		

References

• Marcus du Sautoy: Die Musik der Primzahlen. Auf den Spuren des groessten Raetsels der Mathematik, Beck, Muenchen 2004

Links

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

Crossrefs

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

Programs

Mathematica

Select[Range[2100],AllTrue[{#*10^4+1331,1331*10^IntegerLength[#]+#},PrimeQ]&] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, Aug 21 2015 *)

PARI

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