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 A259043 #13 Jan 23 2022 07:31:20 %S A259043 0,1,2,3,4,5,6,7,8,9,1,3,5,7,9,11,13,15,17,10,2,4,6,8,10,12,14,16,9, %T A259043 12,3,5,7,9,11,13,15,8,11,14,4,6,8,10,12,14,7,10,13,16,5,7,9,11,13,6, %U A259043 9,12,15,18,6,8,10,12,5,8,11,14,17,20,7,9,11,4,7 %N A259043 a(n) = if n < 10 then n else a(floor(n/10) + n mod 10) + n mod 10. %C A259043 a(A259046(n)) = n and a(m) != n for m < A259046(n). %H A259043 Reinhard Zumkeller, <a href="/A259043/b259043.txt">Table of n, a(n) for n = 0..10000</a> %o A259043 (Haskell) %o A259043 a259043 x = if x < 10 then x else a259043 (x' + d) + d %o A259043 where (x', d) = divMod x 10 %o A259043 (PARI) a(n) = if (n<10, n, my(u=n%10); a(n\10 + u) + u); \\ _Michel Marcus_, Jan 23 2022 %Y A259043 Cf. A076314, A007953, A008687, A259046. %K A259043 nonn,base %O A259043 0,3 %A A259043 _Reinhard Zumkeller_, Jun 17 2015