A036519 Smallest triangular number containing exactly n 2's.

21, 1225, 23220, 212226, 22121226, 2202322528, 21222223210, 202222242820, 22122952222920, 229222922294226, 2221228522222920, 222322222025202925, 222212284222222920, 22222122841222222920, 2092226022222222442221, 22222222042522220020225, 622222207421222222222253, 22222212062122272422225226

Offset: 1

Author

David W. Wilson

Keywords

• nonn
• base

Crossrefs

Cf. A048357, A036517-A036526.

Programs

Mathematica

nsmall = Table[Infinity, 20];
For[i = 0, i <= 10^6, i++, p = PolygonalNumber[i];
  n0 = Count[IntegerDigits[p], 2];
  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