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 A036526 #12 Mar 22 2020 17:30:27 %S A036526 91,990,199396,998991,399949903,2919969990,39999939903,999999911791, %T A036526 9999192996990,499798990999990,99597939989199996,999699998689998991, %U A036526 19699899919999499091,999532899999499099996,999999859999976929990,199793999409939999989991,138999999499599999199995,99996999694999999299662991 %N A036526 Smallest triangular number containing exactly n 9's. %t A036526 nsmall = Table[Infinity, 20]; %t A036526 For[i = 0, i <= 10^6, i++, p = PolygonalNumber[i]; %t A036526 n0 = Count[IntegerDigits[p], 9]; %t A036526 If[nsmall[[n0]] > p, nsmall[[n0]] = p]]; %t A036526 ReplaceAll[nsmall, Infinity -> "?"] (* _Robert Price_, Mar 22 2020 *) %Y A036526 Cf. A048364, A036517-A036525. %K A036526 nonn,base %O A036526 1,1 %A A036526 _David W. Wilson_ %E A036526 a(12)-a(18) from _Giovanni Resta_, Oct 30 2019