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A137315 a(n) = least number m such that any finite group of order at least m has at least n automorphisms. 1
1, 3, 7, 7, 13, 13, 19, 19, 31, 31, 31, 31, 43, 43, 43, 43, 61, 61, 61, 61, 67, 67, 67, 67, 91, 91, 91, 91, 91, 91, 91, 91, 121, 121, 121, 121, 127, 127, 127, 127, 151, 151, 151, 151, 151, 151, 151, 151 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(n) <= (n-1)^(n + (n-2)[log_2(n-1)]) for n > 4 [Ledermann, Neumann, Thm. 6.6].

a(n) is odd [MacHale, Sheehy, Thm. 15].

a(2n-1) = a(2n) for 1 < n < 204 [ibid.].

The case of cyclic groups shows that a(n)>=A139795(n). This inequality can be strict: if M denotes the Mathieu group M_{22} of order 2^7.3^2.5.7.11, then Aut(12.M) = M.2, so that a(2^8.3^2.5.7.11 + 1) > 2^9.3^3.5.7.11, but A139795(2^8.3^2.5.7.11 + 1) = 2.3.5.7^2.11.13.23 + 1 < 2^9.3^3.5.7.11.

REFERENCES

John N. Bray and Robert A. Wilson, On the orders of automorphism groups of finite groups, Bull. London Math. Soc. 37 (2005) 381--385.

W. Ledermann, B. H. Neumann, On the order of the automorphism group of a finite group 1, Proc. Roy. Soc. Lon., 233A(1195) (1956), 494-506

D. MacHale, R. Sheehy, Finite groups with few automorphisms, Math. Proc. Roy. Irish Acad., 104A(2) (2004), 231-238

LINKS

Table of n, a(n) for n=1..48.

B. Jubin, Sequences contributed to the OEIS.

EXAMPLE

a(3) = a(4) = 7 because every finite group with at least 7 elements has at least 4 automorphisms while the cyclic group of order 6 has only phi(6)=2 automorphisms.

CROSSREFS

Different from A139795 (see Comments).

Sequence in context: A024612 A227025 A073881 * A139795 A118259 A060845

Adjacent sequences:  A137312 A137313 A137314 * A137316 A137317 A137318

KEYWORD

hard,more,nonn

AUTHOR

Benoit Jubin, Apr 06 2008, May 26 2008

STATUS

approved

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Last modified December 22 05:04 EST 2014. Contains 252328 sequences.