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 A068131 #14 Sep 19 2024 16:34:43 %S A068131 1596,2775,3486,3828,4278,4656,5565,6555,7626,8256,9453,14196,15753, %T A068131 16653,17391,18336,21945,22791,23871,24753,28920,32385,34716,37128, %U A068131 38226,39621,40755,42195,43365,44850,46056,51681,54615,56280,57630 %N A068131 Triangular numbers with sum of digits = 21. %C A068131 1. The sequence is unbounded, as the (5*10^k + 6)-th triangular number is a term. 2. The sum of the digits of triangular numbers in most cases is a triangular number. 3. Conjecture: For every triangular number T there exist infinitely many triangular numbers with sum of digits = T. %H A068131 Harvey P. Dale, <a href="/A068131/b068131.txt">Table of n, a(n) for n = 1..1000</a> %t A068131 Select[Accumulate[Range[400]],Total[IntegerDigits[#]]==21&] (* _Harvey P. Dale_, Jun 06 2015 *) %Y A068131 Subsequence of A000217. %Y A068131 Cf. A068127, A068128, A068129, A068130. %K A068131 base,easy,nonn %O A068131 1,1 %A A068131 _Amarnath Murthy_, Feb 21 2002 %E A068131 More terms from _Sascha Kurz_, Mar 06 2002 %E A068131 Offset changed by _Andrew Howroyd_, Sep 19 2024