A048346 -id:A048346 - cp's OEIS frontend

A048356 a(n) is the index of the smallest triangular number containing exactly n 1's.

1, 18, 58, 458, 1541, 6018, 47141, 149406, 471404, 4756366, 15563541, 149075893, 149004101, 149071198, 14907133333, 47322533981, 471406654834, 1510636363333, 4714049577658, 17954448535733, 471151591552466, 1490649602094141, 4519177339165085, 15434448560354601, 47140495990478741

Offset: 1

Patrick De Geest, Mar 15 1999

Eric Weisstein's World of Mathematics, Triangular Number

Cf. A036518, A048346, A048355, A048357, A048358, A048359, A048360, A048361, A048362, A048363, A048364, A048531.

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 *)

a(15)-a(16) from Lars Blomberg, May 13 2011
a(17)-a(18) from Giovanni Resta, Oct 30 2019
a(19)-a(25) from Max Alekseyev, Mar 07 2025

A036508 Smallest square containing exactly n 1's.

Original entry on oeis.org

1, 121, 11881, 1110916, 11431161, 111112681, 11112111396, 171511111321, 1113111511681, 105111111121641, 6111111111571216, 111611104111115361, 1411111111712116441, 1113101111111117041, 1111116080161111121161, 11111119101145491111121, 516116117111111111421121

Offset: 1

David W. Wilson

a(17) > 4*10^23. - Jon E. Schoenfield, Jan 04 2009

a(20) > 10^28. - Giovanni Resta, Jul 27 2018

Giovanni Resta, Table of n, a(n) for n = 1..19

Cf. A048346.

a[n_] := Block[{k=1}, While[DigitCount[k^2, 10, 1] != n, k++]; k^2]; Array[a, 7] (* Giovanni Resta, Jul 27 2018 *)

a(13)-a(16) from Jon E. Schoenfield, Jan 05 2009

a(17) from Giovanni Resta, Jul 27 2018

cp's OEIS Frontend

A048356 a(n) is the index of the smallest triangular number containing exactly n 1's.

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