A036507 Smallest square containing exactly n decimal digits '0'.

0, 100, 102400, 10000, 10240000, 1000000, 1024000000, 100000000, 102400000000, 10000000000, 10240000000000, 1000000000000, 1024000000000000, 100000000000000, 102400000000000000, 10000000000000000, 10240000000000000000, 1000000000000000000, 1024000000000000000000

Offset

1,2

Links

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

Formula

a(2*n) = 10^(2*n), a(2*n+1) = 1024*10^(2*n) for n >= 1 since 1024 is the smallest square factor that contains a single '0'. - Georg Fischer, Jul 03 2023

Sum_{n>=2} 1/a(n) = 1025/101376. - Amiram Eldar, Aug 26 2025

Mathematica

nsmall = Table[Infinity, 20];
For[i = 0, i <= 4*10^6, i++, n0 = Count[IntegerDigits[i^2], 0];
  If[nsmall[[n0]] > i^2, nsmall[[n0]] = i^2]];
ReplaceAll[nsmall, Infinity -> "?"] (* Robert Price, Mar 22 2020 *)
a[n_] := If[OddQ[n], 1024*10^(n-1), 10^n]; a[1] = 0; Array[a, 20] (* Amiram Eldar, Aug 26 2025 *)

Crossrefs

Cf. A036508 (digits 1), A036509 (2), A036510 (3), A036511 (4), A036512 (5), A036513 (6), A036514 (7), A036515 (8), A036516 (9).

Sequence in context: A151648 A013747 A065447 * A369405 A202055 A185303

Adjacent sequences: A036504 A036505 A036506 * A036508 A036509 A036510

Keyword

nonn,base,easy

Author

David W. Wilson

Status

approved