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 A024850 #19 Jul 26 2019 21:29:08
%S A024850 2,9,21,46,84,135,206,308,429,583,772,987,1265,1552,1906,2308,2767,
%T A024850 3278,3840,4478,5201,5956,6783,7704,8706,9777,10976,12241,13591,14985,
%U A024850 16546,18230,20019,21862,23824,25907,28111,30474,32897,35482,38208,41125,44159,47239,50516,53944
%N A024850 Let c(k) denote the k-th composite number and p(k) the k-th prime number; then a(n) = Sum_{i=n*(n-1)/2+1 .. n*(n+1)/2} c(i) - Sum_{i=1..n} p(i).
%F A024850 a(n) = A072475(n) - A007504(n) [corrected by _Sean A. Irvine_, Jul 26 2019].
%e A024850 a(1) = 4 - 2 = 2.
%e A024850 a(2) = 6 + 8 - 2 - 3 = 9.
%e A024850 a(3) = 9 + 10 + 12 - 2 - 3 - 5 = 21.
%Y A024850 Cf. A071411.
%K A024850 nonn
%O A024850 1,1
%A A024850 _Amarnath Murthy_ and _Benoit Cloitre_, Jun 23 2002
%E A024850 a(7) and a(8) corrected and more terms from _Sean A. Irvine_, Jul 26 2019