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%I #15 Jul 08 2023 14:51:07
%S 3,5,6,8,9,12,30,32,33,46,52,62,74,76,86,98,130,134,154,228,230,242,
%T 256,266,346,352,382,412,428,474,488
%N Numbers n such that A000295(n) = 2^n-n-1 is a semiprime.
%C A candidate for the next term is a(32) = 634. 2^634-635 is composite with 191 decimal digits and unknown factorization. - _Hugo Pfoertner_, Aug 13 2007
%H Dario Alpern, <a href="https://www.alpertron.com.ar/ECM.HTM">Factorization using the Elliptic Curve Method.</a>
%H <a href="http://factordb.com/index.php?query=2%5E634-635">Status of 2^634-635 in factordb.com</a>.
%e a(3) = 6 because 2^6-6-1 = 57 = 3*19 is a semiprime.
%Y Cf. A000295 2^n-n-1 (column 2 of the Eulerian numbers), A099439 2^n-n-1 is prime, A099440 primes in A000295, A099442 semiprimes in A000295.
%K hard,more,nonn
%O 1,1
%A _Hugo Pfoertner_, Oct 18 2004
%E More terms from _Hugo Pfoertner_, Aug 13 2007
%E a(24) corrected by _Hugo Pfoertner_, Sep 07 2017
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