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 A071817 #25 Jul 09 2017 04:53:05 %S A071817 1,3,6,10,15,21,28,36,45,54,61,66,69,70,69,66,61,54,45,36,28,21,15,10, %T A071817 6,3,1 %N A071817 Number of 3-digit numbers whose digits add up to n. %C A071817 The sequence as a whole is palindromic; a(n) = a(28-n). - _Jon E. Schoenfield_, Nov 19 2016 %F A071817 G.f.: (1 - x^10)^2*(x - x^10)/(1 - x)^3. - _Miquel Cerda_, Jul 09 2017 %e A071817 a(4) = 10 because there are 10 different 3-digit numbers whose digit sum is 4 (103, 112, 121, 130, 202, 211, 220, 301, 310, 400, which are the 3-digit elements of A052218). %p A071817 for i from 1 to 9*3 do a[i] := 0:od:for i from 100 to 999 dob := convert(i,base,10): s := sum(b[j],j=1..nops(b)):a[s] := a[s]+1:od:seq(a[j],j=1..3*9); %Y A071817 Cf. A071816. %K A071817 fini,full,nonn,base %O A071817 1,2 %A A071817 _Graeme McRae_, Jun 07 2002 %E A071817 Corrected and extended by _Sascha Kurz_, Feb 07 2003 %E A071817 Name clarified by _Jon E. Schoenfield_, Nov 20 2016