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 A174441 Primes p such that the concatenations p//1331 and 1331//p are both prime numbers (for naturals see A174355). 3
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS See comments and references for A173836, A174213. LINKS Harvey P. Dale, Table of n, a(n) for n = 1..1000 EXAMPLE 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). 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 *) PROG (PARI) isok(n) = isprime(n) && isprime(n*10^4 + 1331) && isprime(1331*10^(length(Str(n))) + n); \\ Michel Marcus, Aug 27 2013 CROSSREFS Cf. A168327, A168417, A173836, A174213, A174260, A174355. Sequence in context: A140042 A239747 A261335 * A094249 A244771 A074836 Adjacent sequences:  A174438 A174439 A174440 * A174442 A174443 A174444 KEYWORD base,nonn AUTHOR Eva-Maria Zschorn (e-m.zschorn(AT)zaschendorf.km3.de), Mar 20 2010 STATUS approved

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Last modified August 11 18:37 EDT 2020. Contains 336428 sequences. (Running on oeis4.)