A048361 a(n) is the index of the smallest triangular number containing exactly n 6's.

3, 11, 36, 363, 3366, 8563, 35963, 394123, 3055048, 11531588, 115464831, 115470036, 1154484036, 10645763163, 35401884036, 152754484036, 365148371588, 2292012515963, 33065591380305, 115470003521836, 642442319075676, 1154701378423588, 10996978373724908, 36347397889274188, 230810167309875091

Offset

1,1

Links

Table of n, a(n) for n=1..25.

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], 6];
  If[nsmall[[n0]] > i, nsmall[[n0]] = i]];
ReplaceAll[nsmall, Infinity -> "?"] (* Robert Price, Mar 22 2020 *)

Crossrefs

Cf. A036523, A048351, A048355, A048356, A048357, A048358, A048359, A048360, A048362, A048363, A048364, A048541.

Sequence in context: A286318 A119054 A119090 * A119161 A119211 A119235

Adjacent sequences: A048358 A048359 A048360 * A048362 A048363 A048364

Keyword

nonn,base,changed

Author

Patrick De Geest, Mar 15 1999

Extensions

a(13)-a(15) from Lars Blomberg, May 16 2011

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

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

Status

approved