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 A069498 #24 Aug 19 2021 16:25:50 %S A069498 0,10,120,190,210,300,630,780,820,990,1540,1770,1830,2080,2850,3160, %T A069498 3240,3570,4560,4950,5050,5460,6670,7140,7260,7750,9180,9730,9870, %U A069498 10440,12090,12720,12880,13530,15400,16110,16290,17020,19110,19900,20100,20910,23220 %N A069498 Triangular numbers of the form 10*k. %C A069498 Intersection of A000217 and A008592. - _Michel Marcus_, Sep 17 2013 %H A069498 Harvey P. Dale, <a href="/A069498/b069498.txt">Table of n, a(n) for n = 1..1000</a> %F A069498 G.f.: -10*x^2*(x^6+11*x^5+7*x^4+2*x^3+7*x^2+11*x+1) / ((x-1)^3*(x+1)^2*(x^2+1)^2). - _Colin Barker_, Sep 23 2013 %p A069498 a[0] := 0:a[1] := 4:a[2] := 15:a[3] := 19:seq((20*(floor(i/4))+a[i mod 4])*(20*(floor(i/4))+a[i mod 4]+1)/2,i=0..100); %t A069498 Select[Accumulate[Range[0,250]],Divisible[#,10]&] (* _Harvey P. Dale_, Aug 28 2016 *) %Y A069498 Cf. A000217, A008592. %K A069498 nonn,easy %O A069498 1,2 %A A069498 _Amarnath Murthy_, Mar 30 2002 %E A069498 Corrected and extended by _Harvey P. Dale_ and _Sascha Kurz_, Mar 31 2002