A108794 - OEIS

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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.

13, 23, 31, 43, 61, 67, 79, 101, 107, 131, 149, 151, 157, 193, 197, 211, 229, 233, 251, 263, 269, 277, 283, 293, 311, 313, 331, 367, 389, 409, 419, 421, 449, 457, 463, 467, 499, 503, 547, 563, 587, 593, 607, 619, 659, 661, 673, 677, 691, 701, 709, 733, 751

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OFFSET

1,1

COMMENTS

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

LINKS

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

EXAMPLE

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

MATHEMATICA

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

CROSSREFS