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A048360 a(n) is the index of the smallest triangular number containing exactly n 5's. 1
5, 10, 105, 714, 5010, 34221, 103494, 317885, 3243010, 1054130, 55708989, 280555005, 1051237885, 5206833885, 30184681729, 105409283410, 1053999578610, 1005540238434 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
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], 5];
If[nsmall[[n0]] > i, nsmall[[n0]] = i]];
ReplaceAll[nsmall, Infinity -> "?"] (* Robert Price, Mar 22 2020 *)
CROSSREFS
Sequence in context: A344140 A267042 A119137 * A357565 A251702 A067958
KEYWORD
nonn,base,more
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
STATUS
approved

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Last modified June 13 17:32 EDT 2024. Contains 373391 sequences. (Running on oeis4.)