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 A067520 #24 Jan 18 2024 04:25:42 %S A067520 1,10,21,45,55,120,171,300,465,666,820,1035,1485,1830,2016,2211,2628, %T A067520 2850,2926,3321,4095,5050,5565,5886,7260,8001,8911,10011,10440,13203, %U A067520 14196,16290,17955,18145,18528,19701,20910,22155,23436,24310,29646 %N A067520 Triangular numbers whose index is a multiple of the sum of their digits. %H A067520 Robert Israel, <a href="/A067520/b067520.txt">Table of n, a(n) for n = 1..10000</a> %e A067520 T(30) = 465 and 30 = 2*(4+6+5). %p A067520 f:= proc(n) local t; %p A067520 t:= n*(n+1)/2; %p A067520 if n mod convert(convert(t,base,10),`+`) = 0 then return t fi %p A067520 end proc: %p A067520 map(f, [$1..300]); # _Robert Israel_, Jan 18 2024 %t A067520 PolygonalNumber[Select[Range[300], Divisible[#, Total[IntegerDigits[# (# + 1) / 2]]]&]] (* _Paolo Xausa_, Jan 18 2024 *) %Y A067520 Includes A037156. %K A067520 base,easy,nonn %O A067520 1,2 %A A067520 _Amarnath Murthy_, Feb 14 2002 %E A067520 More terms from _Sascha Kurz_, Mar 18 2002 %E A067520 Offset corrected by _Sean A. Irvine_, Dec 17 2023