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 A068128 #14 Sep 17 2024 19:06:39 %S A068128 6,15,105,231,2211,3003,20301,112101,2003001,122000010,200030001, %T A068128 20000300001,2000003000001,200000030000001,20000000300000001, %U A068128 2000000003000000001,200000000030000000001,20000000000300000000001,2000000000003000000000001 %N A068128 Triangular numbers with sum of digits = 6. %C A068128 1. The sequence is unbounded, as the (2*10^k +1)-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. %t A068128 Select[Accumulate[Range[20000002]],Total[IntegerDigits[#]]==6&] (* _Harvey P. Dale_, Jun 05 2012 *) %Y A068128 Intersection of A000217 and A052220. %Y A068128 Cf. A068127. %K A068128 base,easy,nonn %O A068128 1,1 %A A068128 _Amarnath Murthy_, Feb 21 2002 %E A068128 More terms from _Sascha Kurz_, Mar 06 2002 %E A068128 More terms from _Sean A. Irvine_, Mar 17 2023 %E A068128 Offset changed by _Andrew Howroyd_, Sep 17 2024