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 A099441 #21 Jan 05 2025 10:00:25 %S A099441 3,5,6,8,9,12,30,32,33,46,52,62,74,76,86,98,130,134,154,228,230,242, %T A099441 256,266,346,352,382,412,428,474,488,634,650,662,688,704,722,772,896, %U A099441 986,1108,1222,1246,1326 %N A099441 Numbers n such that A000295(n) = 2^n-n-1 is a semiprime. %C A099441 A candidate for the next term is a(45) = 1736. 2^1736-1737 is composite with 523 decimal digits and unknown factorization. - _Tyler Busby_, Jan 05 2025 %H A099441 Dario Alpern, <a href="https://www.alpertron.com.ar/ECM.HTM">Factorization using the Elliptic Curve Method.</a> %H A099441 <a href="http://factordb.com/index.php?query=2%5E1736-1737">Status of 2^1736-1737 in factordb.com</a>. %e A099441 a(3) = 6 because 2^6-6-1 = 57 = 3*19 is a semiprime. %Y A099441 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 A099441 hard,more,nonn %O A099441 1,1 %A A099441 _Hugo Pfoertner_, Oct 18 2004 %E A099441 More terms from _Hugo Pfoertner_, Aug 13 2007 %E A099441 a(24) corrected by _Hugo Pfoertner_, Sep 07 2017 %E A099441 a(32)-a(44) from _Tyler Busby_, Jan 05 2025