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 A108794 Primes whose 10's complement is a semiprime, i.e., p is prime and 10^L - p is a semiprime, where L is the number of digits in p. 1

%I

%S 13,23,31,43,61,67,79,101,107,131,149,151,157,193,197,211,229,233,251,

%T 263,269,277,283,293,311,313,331,367,389,409,419,421,449,457,463,467,

%U 499,503,547,563,587,593,607,619,659,661,673,677,691,701,709,733,751

%N Primes whose 10's complement is a semiprime, i.e., p is prime and 10^L - p is a semiprime, where L is the number of digits in p.

%C Some twin prime terms are (149,151), (311,313), (419,421), (659,661), ... Conjecture: there are infinitely many twin primes in this sequence.

%H Harvey P. Dale, <a href="/A108794/b108794.txt">Table of n, a(n) for n = 1..1000</a>

%e 563 is a term because it is prime and 10^3 - 563 = 437 = 19*23.

%t Select[Prime[Range[200]],PrimeOmega[10^IntegerLength[#]-#]==2&] (* _Harvey P. Dale_, Oct 13 2011 *)

%K easy,nonn,base

%O 1,1

%A _Jason Earls_, Jul 09 2005

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Last modified May 6 16:03 EDT 2021. Contains 343586 sequences. (Running on oeis4.)