OFFSET
1,2
COMMENTS
The solvability of a group whose order is a(n) can be reduced to the solvability of smaller group using the Sylow theorems, provided the order is not a prime.
80 is not a member of this sequence, but is a member of A168186. - Franklin T. Adams-Watters, Jan 26 2010
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
PROG
(PARI) is(n)=if(n<12, return(n>0)); my(f=factor(n)); for(i=1, #f~, fordiv(n/f[i, 1]^f[i, 2], d, if(d>1&&d%f[i, 1]==1, next(2))); return(1)); 0 \\ Charles R Greathouse IV, Oct 27 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Masahiko Shin, May 14 2009
EXTENSIONS
Corrected by Charles R Greathouse IV, Oct 27 2013
STATUS
approved