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A085777 Semiprimes such that when they are concatenated with their reversal are semiprime. 0

%I #7 Dec 15 2017 17:36:29

%S 14,34,38,74,91,94,115,146,169,185,194,305,334,341,346,355,361,362,

%T 386,394,395,398,706,721,731,745,755,766,794,799,901,923,926,955,974,

%U 985,1027,1046,1094,1138,1141,1147,1174,1195,1202,1238,1247,1261,1262,1271

%N Semiprimes such that when they are concatenated with their reversal are semiprime.

%C This is to A001358 = semiprimes (or biprimes): products of two primes, as A054217 is to primes A000040. Note that a subsequence is the emirpimes (A097393) which, when concatenated with their digital reversals, become different semiprimes. Examples of this subsequence: 94, 115, 169, 185, ... because 9449 = 11 * 859, 115511 = 11 * 10501, 169961 = 11 * 15451, 185581 = 11 * 16871. [From _Jonathan Vos Post_, Apr 05 2010]

%F {positive integers s = p*q in A001358, p and q primes, such that Concatenate(s, R(s)) = u*v is in A001358, u and v primes} = {positive integers s = p*q in A001358, p and q primes, such that Concatenate(s, A004086(s)) = u*v is in A001358, u and v primes}. [From _Jonathan Vos Post_, Apr 05 2010]

%e a(7)=115 because 115511 = 11*10501.

%Y Cf. A001358.

%Y Cf. A000040, A001358, A004086, A097393 [From _Jonathan Vos Post_, Apr 05 2010]

%K base,nonn

%O 1,1

%A _Jason Earls_, Jul 23 2003

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Last modified March 28 05:39 EDT 2024. Contains 371235 sequences. (Running on oeis4.)