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 A013921 #24 Nov 26 2022 13:21:03
%S A013921 4,10,18,27,49,63,78,94,112,132,153,175,224,250,305,335,400,434,469,
%T A013921 505,543,582,622,664,708,753,799,847,896,946,1158,1214,1271,1329,1389,
%U A013921 1514,1578,1643,1846,1916,1988,2062,2290,2368,2448,2529,2611,2695,2780,2866
%N A013921 Composite numbers that are equal to the sum of the first k composites for some k.
%H A013921 Harvey P. Dale, <a href="/A013921/b013921.txt">Table of n, a(n) for n = 1..10000</a>
%F A013921 a(n) = A053767(A013919(n)). [Found by LODA miner] - _Christian Krause_, Nov 24 2022
%t A013921 Module[{nn=100,comps},comps=Complement[Range[4,nn],Prime[ Range[ PrimePi[ nn]]]]; Select[Accumulate[comps],!PrimeQ[#]&]] (* _Harvey P. Dale_, May 21 2014 *)
%o A013921 (PARI) isok(c) = if ((c>1) && !isprime(c), my(s=0); forcomposite(x=1, oo, s+=x; if (s == c, return(1)); if (s > c, return(0)))); \\ _Michel Marcus_, Nov 25 2022
%Y A013921 Cf. A013919, A013920, A053767.
%K A013921 nonn
%O A013921 1,1
%A A013921 _N. J. A. Sloane_, _Henri Lifchitz_
%E A013921 More terms from _David W. Wilson_
%E A013921 Name edited by _Michel Marcus_, Nov 25 2022