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A101618
Indices of semiprimes in A001003.
1
7, 11, 17, 19, 21, 239
OFFSET
1,1
COMMENTS
No more terms < 2000. - David Wasserman, Mar 27 2008
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
LINKS
Eric Weisstein's World of Mathematics, Semiprime.
FORMULA
A001003(a(n)) is in A001358 (semiprimes).
EXAMPLE
a(1) = 7 because A001003(7) = 4279 = 11 * 389.
a(2) = 11 because A001003(11) = 2646723 = 3 * 882241.
a(3) = 17 because A001003(17) = 55909013009 = 41263 * 1354943.
a(4) = 19 because A001003(19) = 1618362158587 = 24413 * 66290999.
a(5) = 21 because A001003(21) = 47574827600981 = 3253 * 14624908577.
CROSSREFS
KEYWORD
nonn,more,less
AUTHOR
Jonathan Vos Post, Dec 09 2004
EXTENSIONS
Edited by Franklin T. Adams-Watters, Nov 07 2006
Changed by Michael Somos, Mar 31 2007, because of the re-indexing of A001003.
a(6) from David Wasserman, Mar 27 2008
STATUS
approved