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 A271641 #15 Jun 02 2025 12:17:45 %S A271641 9,17,15,13,11,9,7,5,3,1,17,32,29,25,21,17,13,9,5,2,15,28,26,23,19,15, %T A271641 11,7,4,2,13,24,22,20,17,13,9,6,4,2,11,20,18,16,14,11,8,6,4,2,9,16,14, %U A271641 12,10,9,8,6,4,2,7,12,10,8,7,7,7,6,4,2,5,8,6,5,5,5,5,5,4,2,3,4,3,3,3,3,3,3,3,2,1,1,1,1,1,1,1,1,1,1,17,32 %N A271641 Quantity of ancestors for n (in the sense explained below). %C A271641 See A271639 for the definition of an ancestor. %e A271641 "0" has 9 ancestors, which are 11, 22, 33, 44, 55, 66, 77, 88 and 99; "1" has 17 ancestors, which are 10, 12, 21, 23, 32, 34, 43, 45, 54, 56, 65, 67, 76, 78, 87, 89, 98; "2" has 15 ancestors, which are 13, 20, 24, 31, 35, 42, 46, 53, 57, 64, 68, 75, 79, 86, 97; "3" has 13 ancestors, etc. Thus the sequence starts with 9, 17, 15, 13, etc. %Y A271641 Cf. A271639. %K A271641 nonn,base %O A271641 0,1 %A A271641 _Eric Angelini_ and _Jean-Marc Falcoz_, Apr 11 2016