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 A158031 #9 Jul 07 2023 14:40:50 %S A158031 1,2,3,4,8,9,11,12,14,17,22,25,30,33,36,38,41,43,46,48,51,53,56,58,61, %T A158031 63,65,66,69,74,77,78,81,86,89,90,93,98,101,102,105,110,113,114,117, %U A158031 122,125,126,132,133,139,140,146,147,153,154,160,161,167,168,174,175,181 %N A158031 Sides of equilateral triangles which are filled exactly (no holes, no overlaps) by the digits used to write a subsequence of consecutive triangular numbers, starting with 0. %C A158031 The triangular numbers fitting exactly in a "triangulars-digits triangle" are given by A158030. Terms computed by Jean-Marc Falcoz. %H A158031 Eric Angelini, <a href="http://www.cetteadressecomportecinquantesignes.com/DigitSpiral.htm">Digit Spiral</a> %H A158031 E. Angelini, <a href="/A158022/a158022.pdf">Digit Spiral</a> [Cached copy, with permission] %e A158031 ...0....0....0.....0 %e A158031 ........13...13....13 %e A158031 .............610...610 %e A158031 ...................1521 %e A158031 The above "equilateral" triangles, filled exactly by a subsequence of consecutive triangular numbers starting with 0 have sides 1, 2, 3, 4. The next properly filled triangle will have side 8. %K A158031 base,nonn %O A158031 1,2 %A A158031 _Eric Angelini_, Mar 11 2009