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 A158338 #16 Sep 08 2022 08:45:42 %S A158338 6,15,16,21,27,33,35,51,57,65,77,87,93,105,111,135,141,143,155,161, %T A158338 165,177,183,185,189,201,203,215,231,237,245,267,275,285,287,321,335, %U A158338 341,345,357,371,375,377,393,413,425,429,437,447,453,465,471 %N A158338 Composite numbers k such that k - number of divisors of k = prime. %C A158338 Subsequence of A067531. - _Michel Marcus_, Dec 22 2014 %H A158338 Amiram Eldar, <a href="/A158338/b158338.txt">Table of n, a(n) for n = 1..10000</a> %e A158338 6 is composite and has 4 divisors (1, 2, 3, 6); 6 - 4 = 2, which is prime, so 6 is in the sequence. %e A158338 15 is composite and has 4 divisors (1, 3, 5, 15); 15 - 4 = 11, which is prime, so 15 is in the sequence. %e A158338 16 is composite and has 5 divisors (1, 2, 4, 8, 16); 16 - 5 = 11, which is prime, so 16 is in the sequence. %t A158338 Select[Range[500], CompositeQ[#] && PrimeQ[# - DivisorSigma[0, #]] &] (* _Amiram Eldar_, Jul 16 2019 *) %o A158338 (Magma) [k:k in [1..500]|not IsPrime(k) and IsPrime(k-#Divisors(k))]; // _Marius A. Burtea_, Jul 16 2019 %Y A158338 Cf. A000005, A000040, A002808, A035004, A067531. %K A158338 nonn %O A158338 1,1 %A A158338 _Juri-Stepan Gerasimov_, Mar 16 2009, Nov 14 2009 %E A158338 Extended by _R. J. Mathar_, May 19 2010