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A036524 Smallest triangular number containing exactly n 7's. 1
78, 1770, 72771, 6787770, 37779778, 2476777771, 7477727778, 7077757275771, 27778877747778, 177775772774775, 7777755777787716, 172777077787777785, 7987777777779277726, 177577777275777787371, 377679777777377717778, 77773137747757777775775, 777367777737777774977796, 67775787670776777773777778 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

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

MATHEMATICA

nsmall = Table[Infinity, 20];

For[i = 0, i <= 10^6, i++, p = PolygonalNumber[i];

  n0 = Count[IntegerDigits[p], 7];

  If[nsmall[[n0]] > p, nsmall[[n0]] = p]];

ReplaceAll[nsmall, Infinity -> "?"] (* Robert Price, Mar 22 2020 *)

CROSSREFS

Cf. A048362, A036517-A036526.

Sequence in context: A160839 A187590 A172217 * A262063 A140934 A133239

Adjacent sequences:  A036521 A036522 A036523 * A036525 A036526 A036527

KEYWORD

nonn,base

AUTHOR

David W. Wilson

EXTENSIONS

a(13)-a(18) from Giovanni Resta, Oct 30 2019

STATUS

approved

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Last modified September 24 03:15 EDT 2021. Contains 347623 sequences. (Running on oeis4.)