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A240007 Smallest k such that the number of groups of order k is equal to prime(n), or 0 if no such k exists. 0
4, 75, 8, 375, 140, 56, 675, 1029, 294, 1380, 0, 180, 420, 112, 120, 656, 6875, 312, 243, 3660, 0, 3612, 0, 4140, 6498, 0, 0, 0, 0, 810, 0, 1260, 792, 0, 0, 0, 0, 0, 1936, 0, 1456, 1320, 0, 0, 144, 1000, 1368, 0, 1404, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Smallest k such that A000001(k) = prime(n), or 0 if no such k exists.

It seems that there is no order for which the number of groups is 31, 59, 71, 73, 79, 83, 89, 97, 101, 103, 109, 127, 139,...

Above comment is incorrect. According to the Conway article, every n <= 10000000 is the number of groups of order k for some k. So all the 0 entries above are wrong, but we do not necessarily know the true value. - Eric M. Schmidt, Sep 14 2014

LINKS

Table of n, a(n) for n=1..68.

John H. Conway, Heiko Dietrich and E. A. O'Brien, Counting groups: gnus, moas and other exotica, The Mathematical Intelligencer, Spring 2008, Volume 30, Issue 2, pp 6-15, doi:10.1007/BF02985731.

EXAMPLE

a(6)= 56 because prime(6) = 13 => there exists 13 groups of order 56.

MATHEMATICA

lst={}; Do[k=1; While[!FiniteGroupCount[k]==Prime[n], k++]; If[k==2048, AppendTo[lst, 0], AppendTo[lst, k]], {n, 1, 70}]; lst

CROSSREFS

Cf. A000001, A046057, A053403.

Sequence in context: A100865 A007157 A000857 * A046057 A280889 A257367

Adjacent sequences:  A240004 A240005 A240006 * A240008 A240009 A240010

KEYWORD

nonn

AUTHOR

Michel Lagneau, Mar 30 2014

EXTENSIONS

Values for 59, 71, 79, 89, and 97 filled in from Conway link by Eric M. Schmidt, Sep 14 2014

STATUS

approved

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Last modified May 15 04:03 EDT 2021. Contains 343909 sequences. (Running on oeis4.)