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A226143 a(n) is the smallest k > 0 such that A000793(n)^k >= n!. 2
1, 1, 2, 3, 3, 4, 4, 4, 5, 5, 6, 5, 6, 6, 6, 7, 7, 7, 7, 8, 8, 9, 8, 9, 9, 9, 9, 9, 10, 9, 10, 10, 10, 10, 11, 11, 11, 11, 11, 11, 12, 12, 12, 12, 12, 13, 12, 13, 12, 13, 13, 13, 13, 13, 14, 14, 14, 14, 14, 14, 14, 15, 15, 15, 15, 15, 15, 15, 16, 15, 16, 16 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

This is a lower bound for A226142(n), the least positive integer k such that S_n is a product of k cyclic groups. Clearly also a(n) = ceiling(log_m(n!) where m = A000793(n).

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..10000

MAPLE

A000793:=

[1, 2, 3, 4, 6, 6, 12, 15, 20, 30, 30, 60, 60, 84, 105, 140,

210, 210, 420, 420, 420, 420, 840, 840, 1260, 1260, 1540,

2310, 2520, 4620, 4620, 5460, 5460, 9240, 9240, 13860,

13860, 16380, 16380, 27720, 30030, 32760, 60060, 60060,

60060, 60060, 120120]:

a:=proc(n)

global A000793;

local k;

for k from 1 do

if A000793[n]^k >= n! then return k; fi;

od;

end;

MATHEMATICA

b[n_, i_] := b[n, i] = Module[{p}, p = If[i < 1, 1, Prime[i]]; If[n == 0 || i < 1, 1, Max[b[n, i - 1], Table[p^j b[n - p^j, i - 1], {j, 1, Log[p, n] // Floor}]]]];

a[n_] := Module[{m}, If[n == 1, 1, m = b[n, If[n < 8, 3, PrimePi[Ceiling[ 1.328 Sqrt[n Log[n] // Floor]]]]]; Log[m, n!] // Ceiling]];

Array[a, 100] (* Jean-François Alcover, Nov 12 2020, after Alois P. Heinz in A000793 *)

CROSSREFS

Cf. A000793, A226142.

Sequence in context: A189641 A189672 A058889 * A166724 A110862 A104257

Adjacent sequences:  A226140 A226141 A226142 * A226144 A226145 A226146

KEYWORD

nonn

AUTHOR

W. Edwin Clark, May 27 2013

STATUS

approved

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Last modified March 8 08:35 EST 2021. Contains 341942 sequences. (Running on oeis4.)