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

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], 4];
  If[nsmall[[n0]] > i, nsmall[[n0]] = i]];
ReplaceAll[nsmall, Infinity -> "?"] (* Robert Price, Mar 22 2020 *)

Crossrefs

Cf. A036521, A048355-A049364.

Sequence in context: A163951 A231658 A034992 * A307961 A099297 A057782

Adjacent sequences: A048356 A048357 A048358 * A048360 A048361 A048362

Keyword

nonn,base,more

Author

Patrick De Geest, Mar 15 1999

Extensions

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

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

Status

approved