A048359 a(n) is the index of the smallest triangular number containing exactly n 4's.

9, 94, 537, 1043, 29238, 28790, 94238, 942703, 2967970, 45748113, 170565790, 939618480, 2981759361, 29814031731, 94285146809, 298802358238, 2837045748113, 9428516473384, 29810549959517, 537482082424790, 699205897721757, 2974721655733337, 29032426496744790, 29814339990932029, 1043498506508221519

Offset: 1

Author

Patrick De Geest, Mar 15 1999

Keywords

• nonn
• base

Links

• Eric Weisstein's World of Mathematics, Triangular Number

Crossrefs

Cf. A036521, A048349, A048355, A048356, A048357, A048358, A048360, A048361, A048362, A048363, A048364, A048537.

Programs

Mathematica

nsmall = Table[Infinity, 20];
For[i = 0, i <= 10^6, i++, p = PolygonalNumber[i];
  n0 = Count[IntegerDigits[p], 4];
  If[nsmall[[n0]] > i, nsmall[[n0]] = i]];
ReplaceAll[nsmall, Infinity -> "?"] (* Robert Price, Mar 22 2020 *)

Extensions

a(13)-a(14) from Lars Blomberg, May 13 2011

a(15)-a(18) from Giovanni Resta, Oct 30 2019

a(19)-a(25) from Max Alekseyev, Mar 07 2025