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A036518 Smallest triangular number containing exactly n 1's. 1
1, 171, 1711, 105111, 1188111, 18111171, 1111160511, 11161151121, 111111101310, 11311511141161, 121111912011111, 11111811011411671, 11101111131911151, 11111111111113201, 111111312111373411111, 1119711111215111121171, 111112117111126711111195, 1141011111112731111616111 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

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

FORMULA

a(n) = A000217(A048356(n)). - Michel Marcus, Aug 12 2014

MAPLE

P := proc(q, h) local a, b, c, k, n; c:=0; for n from 1 to q do a:=0; b:=n*(n+1)/2;

for k from 1 to ilog10(n*(n+1)/2)+1 do if (b mod 10)=h then a:=a+1; fi; b:=trunc(b/10);

od; if a>c then c:=a; print(n*(n+1)/2); fi; od; end: P(10^9, 1); # Paolo P. Lava, Aug 08 2014

MATHEMATICA

nsmall = Table[Infinity, 20];

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

  n0 = Count[IntegerDigits[p], 1];

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

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

CROSSREFS

Cf. A048356, A036517-A036526.

Sequence in context: A220869 A251329 A221754 * A187133 A185838 A199902

Adjacent sequences:  A036515 A036516 A036517 * A036519 A036520 A036521

KEYWORD

nonn,base

AUTHOR

David W. Wilson

EXTENSIONS

Definition clarified by Robert Israel, Aug 10 2014

a(15)-a(16) from A048356 by Michel Marcus, Aug 12 2014

a(17)-a(18) from Giovanni Resta, Oct 30 2019

STATUS

approved

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Last modified December 2 06:44 EST 2020. Contains 338868 sequences. (Running on oeis4.)