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 A075359 #9 Jul 11 2023 10:07:58
%S A075359 1,5,15,25,20,39,49,53,72,91,113,141,160,137,102,121,161,207,253,203,
%T A075359 168,223,290,354,202,287,369,388,293,393,502,362,444,571,440,531,649,
%U A075359 509,672,655,659,813,670,881,441,505,473,537,556,605,633,697,692,801
%N A075359 Sum of the digits of the next n numbers.
%H A075359 Harvey P. Dale, <a href="/A075359/b075359.txt">Table of n, a(n) for n = 1..1000</a>
%F A075359 a(n) = A037123(n*(n+1)/2)-A037123(n*(n-1)/2). - _David Wasserman_, Jan 16 2005
%e A075359 a(5) = digit sum of 11,12,13,14 and 15 = 20.
%t A075359 Total[Flatten[IntegerDigits/@#]]&/@With[{nn=60},TakeList[Range[(nn(nn+1))/2],Range[ nn]]] (* _Harvey P. Dale_, Jul 11 2023 *)
%Y A075359 Cf. A037123.
%K A075359 nonn,base
%O A075359 1,2
%A A075359 _Amarnath Murthy_, Sep 19 2002
%E A075359 More terms from _David Wasserman_, Jan 16 2005