This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A101618 #25 Feb 16 2025 08:32:55 %S A101618 7,11,17,19,21,239 %N A101618 Indices of semiprimes in A001003. %C A101618 No more terms < 2000. - _David Wasserman_, Mar 27 2008 %C A101618 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 A101618 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Semiprime.html">Semiprime</a>. %F A101618 A001003(a(n)) is in A001358 (semiprimes). %e A101618 a(1) = 7 because A001003(7) = 4279 = 11 * 389. %e A101618 a(2) = 11 because A001003(11) = 2646723 = 3 * 882241. %e A101618 a(3) = 17 because A001003(17) = 55909013009 = 41263 * 1354943. %e A101618 a(4) = 19 because A001003(19) = 1618362158587 = 24413 * 66290999. %e A101618 a(5) = 21 because A001003(21) = 47574827600981 = 3253 * 14624908577. %Y A101618 Cf. A001003, A001358. %Y A101618 Cf. A101619, A092839, A092840. %K A101618 nonn,more,less %O A101618 1,1 %A A101618 _Jonathan Vos Post_, Dec 09 2004 %E A101618 Edited by _Franklin T. Adams-Watters_, Nov 07 2006 %E A101618 Changed by _Michael Somos_, Mar 31 2007, because of the re-indexing of A001003. %E A101618 a(6) from _David Wasserman_, Mar 27 2008