A036518 Smallest triangular number containing exactly n 1's.

1, 171, 1711, 105111, 1188111, 18111171, 1111160511, 11161151121, 111111101310, 11311511141161, 121111912011111, 11111811011411671, 11101111131911151, 11111111111113201, 111111312111373411111, 1119711111215111121171, 111112117111126711111195, 1141011111112731111616111

Offset

1,2

Links

Table of n, a(n) for n=1..18.

Formula

a(n) = A000217(A048356(n)). - Michel Marcus, Aug 12 2014

Mathematica

nsmall = Table[Infinity, 20];
For[i = 0, i <= 10^6, i++, p = PolygonalNumber[i];
  n0 = Count[IntegerDigits[p], 1];
  If[nsmall[[n0]] > p, nsmall[[n0]] = p]];
ReplaceAll[nsmall, Infinity -> "?"] (* Robert Price, Mar 22 2020 *)

Crossrefs

Cf. A048356, A036517-A036526.

Sequence in context: A220869 A251329 A221754 * A187133 A185838 A199902

Adjacent sequences: A036515 A036516 A036517 * A036519 A036520 A036521

Keyword

nonn,base

Author

David W. Wilson

Extensions

Definition clarified by Robert Israel, Aug 10 2014

a(15)-a(16) from A048356 by Michel Marcus, Aug 12 2014

a(17)-a(18) from Giovanni Resta, Oct 30 2019

Status

approved