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A048357
a(n) is the index of the smallest triangular number containing exactly n 2's.
1
6, 49, 215, 651, 6651, 66367, 206020, 635959, 6651759, 21411348, 66651759, 666816649, 666651759, 6666651759, 64687340681, 210818509825, 1115546688777, 6666665142651
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], 2];
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(14)-a(15) from Lars Blomberg, May 13 2011
a(16)-a(18) from Giovanni Resta, Oct 30 2019
STATUS
approved