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A048356
a(n) is the index of the smallest triangular number containing exactly n 1's.
1
1, 18, 58, 458, 1541, 6018, 47141, 149406, 471404, 4756366, 15563541, 149075893, 149004101, 149071198, 14907133333, 47322533981, 471406654834, 1510636363333
OFFSET
1,2
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], 1];
If[nsmall[[n0]] > i, nsmall[[n0]] = i]];
ReplaceAll[nsmall, Infinity -> "?"] (* Robert Price, Mar 22 2020 *)
CROSSREFS
KEYWORD
nonn,base,more
AUTHOR
Patrick De Geest, Mar 15 1999
EXTENSIONS
a(15)-a(16) from Lars Blomberg, May 13 2011
a(17)-a(18) from Giovanni Resta, Oct 30 2019
STATUS
approved