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%I #24 Feb 09 2023 04:36:25
%S 7,11,17,19,21,239
%N Indices of semiprimes in A001003.
%C No more terms < 2000. - _David Wasserman_, Mar 27 2008
%C a(7) >= 4377. A001003(4377) is a 3345-digit composite number with unknown factorization. Other possible terms are 4391, 45207, 45369, 45377, 131723, 131733, ... - _Tyler Busby_, Feb 08 2023
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Semiprime.html">Semiprime</a>.
%F A001003(a(n)) is in A001358 (semiprimes).
%e a(1) = 7 because A001003(7) = 4279 = 11 * 389.
%e a(2) = 11 because A001003(11) = 2646723 = 3 * 882241.
%e a(3) = 17 because A001003(17) = 55909013009 = 41263 * 1354943.
%e a(4) = 19 because A001003(19) = 1618362158587 = 24413 * 66290999.
%e a(5) = 21 because A001003(21) = 47574827600981 = 3253 * 14624908577.
%Y Cf. A001003, A001358.
%Y Cf. A101619, A092839, A092840.
%K nonn,more,less
%O 1,1
%A _Jonathan Vos Post_, Dec 09 2004
%E Edited by _Franklin T. Adams-Watters_, Nov 07 2006
%E Changed by _Michael Somos_, Mar 31 2007, because of the re-indexing of A001003.
%E a(6) from _David Wasserman_, Mar 27 2008
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