A161758 - OEIS

%I #5 Jun 16 2013 03:24:09

%S 4,4,5,4,5,4,5,6,7,4,5,4,5,6,7,4,5,4,5,6,7,4,5,6,7,8,9,4,5,4,5,6,7,8,

%T 9,4,5,6,7,4,5,4,5,6,7,4,5,6,7,8,9,4,5,6,7,8,9,4,5,4,5,6,7,8,9,4,5,6,

%U 7,4,5,4,5,6,7,8,9,4,5,6,7,4,5,6,7,8,9,4,5,6,7,8,9,10,11,4

%N a(n)=n-p+1 where p is the maximal prime less than n-2.

%C By a theorem of Jordan from 1873, a permutation group of degree n is alternating or symmetric if it is a(n)-transitive. For example, a permutation group of degree 100 is alternating or symmetric if it is 4-transitive, since a(100)=100-97+1=4.

%D Camille Jordan, Oeuvres, Volume I, 57.

%o (PARI) a(n) = n - precprime(n-3) + 1 \\ _Michel Marcus_, Jun 16 2013

%K nonn

%O 5,1

%A _David Brink_, Jun 18 2009