A036526 Smallest triangular number containing exactly n 9's.

91, 990, 199396, 998991, 399949903, 2919969990, 39999939903, 999999911791, 9999192996990, 499798990999990, 99597939989199996, 999699998689998991, 19699899919999499091, 999532899999499099996, 999999859999976929990, 199793999409939999989991, 138999999499599999199995, 99996999694999999299662991

Offset: 1

Author

David W. Wilson

Keywords

• nonn
• base

Crossrefs

Cf. A048364, A036517-A036525.

Programs

Mathematica

nsmall = Table[Infinity, 20];
For[i = 0, i <= 10^6, i++, p = PolygonalNumber[i];
  n0 = Count[IntegerDigits[p], 9];
  If[nsmall[[n0]] > p, nsmall[[n0]] = p]];
ReplaceAll[nsmall, Infinity -> "?"] (* Robert Price, Mar 22 2020 *)

Extensions

a(12)-a(18) from Giovanni Resta, Oct 30 2019