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 A243021 #10 Jun 02 2014 22:50:04 %S A243021 12,15,18,21,24,27,30,32,33,36,37,39,45,47,51,52,54,57,58,59,62,63,69, %T A243021 72,81,84,90,96,99,101,103,107,109,111,114,115,117,119,120,123,126, %U A243021 129,135,141,144,147,153,159,161,162,163,169,171,173,174,180,184,185,186,189,197,199,201,204,207,210,213,216,219,221,225,226,231,234,236,237 %N A243021 Numbers n such that n appears in the sequence beginning with the digit-sum of n and extended by adding successive digit-sums. %C A243021 Numbers n>9 with following property: form a sequence b(i) whose initial term is digit-sum(n). Later terms are given by the rule that b(i) = b(i-1) + digit-sum(b(i-1)) and n itself appears in the sequence. %F A243021 b(i) = b(i-1) + digit-sum(b(i-1)) %e A243021 When n = 0..9, the sequence immediately produces n. The sequence for 12 is seeded with digital-sum(12) = 3, 3 + 3 = 6, 6 + 6 = 12. 15 yields 6, 6 + 6 = 12, 12 + 3 = 15. 18 yields 9, 9 + 9 = 18. 21 yields 3, 3 + 3 = 6, 6 + 6 = 12, 12 + 3 = 15, 15 + 6 = 21. %Y A243021 Cf. A007629, A243140. %K A243021 nonn,base,easy %O A243021 1,1 %A A243021 _Anthony Sand_, May 29 2014 %E A243021 Added comments based on those for A007629.