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A085777 Semiprimes such that when they are concatenated with their reversal are semiprime. 0
14, 34, 38, 74, 91, 94, 115, 146, 169, 185, 194, 305, 334, 341, 346, 355, 361, 362, 386, 394, 395, 398, 706, 721, 731, 745, 755, 766, 794, 799, 901, 923, 926, 955, 974, 985, 1027, 1046, 1094, 1138, 1141, 1147, 1174, 1195, 1202, 1238, 1247, 1261, 1262, 1271 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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]

LINKS

Table of n, a(n) for n=1..50.

FORMULA

{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]

EXAMPLE

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

CROSSREFS

Cf. A001358.

Cf. A000040, A001358, A004086, A097393 [From Jonathan Vos Post, Apr 05 2010]

Sequence in context: A112878 A175559 A158899 * A329062 A072566 A039449

Adjacent sequences:  A085774 A085775 A085776 * A085778 A085779 A085780

KEYWORD

base,nonn

AUTHOR

Jason Earls, Jul 23 2003

STATUS

approved

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Last modified November 30 13:47 EST 2021. Contains 349420 sequences. (Running on oeis4.)