A048358 a(n) is the index of the smallest triangular number containing exactly n 3's.

2, 77, 257, 2570, 816, 25808, 163299, 812816, 2463060, 24629808, 246306030, 791999183, 812812816, 2581876578, 81649658057, 247924719918, 812812812816, 8128140492564

Offset

1,1

Links

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

Eric Weisstein's World of Mathematics, Triangular Number

Mathematica

nsmall = Table[Infinity, 20];
For[i = 0, i <= 10^6, i++, p = PolygonalNumber[i];
  n0 = Count[IntegerDigits[p], 3];
  If[nsmall[[n0]] > i, nsmall[[n0]] = i]];
ReplaceAll[nsmall, Infinity -> "?"] (* Robert Price, Mar 22 2020 *)

Crossrefs

Cf. A036520, A048355-A049364.

Sequence in context: A266877 A301472 A041721 * A124456 A338588 A364696

Adjacent sequences: A048355 A048356 A048357 * A048359 A048360 A048361

Keyword

nonn,base,more

Author

Patrick De Geest, Mar 15 1999

Extensions

a(12) corrected by Lars Blomberg, May 13 2011

a(13)-a(15) from Lars Blomberg, May 13 2011

a(16)-a(18) from Giovanni Resta, Oct 30 2019

Status

approved