OFFSET
1,1
COMMENTS
Semiprimes pq with p<q and gcd(p,q-1)=1. - T. D. Noe, Oct 08 2008
REFERENCES
D. S. Dummit and R. M. Foote, Abstract Algebra, Wiley, 3rd Edition, 2003, page 135.
LINKS
T. D. Noe, Table of n, a(n) for n=1..1000
John H. Conway, Heiko Dietrich and E. A. O'Brien, Counting groups: gnus, moas and other exotica.
MATHEMATICA
Select[Select[Range[1000], FactorInteger[#][[All, 2]] == {1, 1} &], !
Divisible[FactorInteger[#][[2, 1]] - 1, FactorInteger[#][[1, 1]]] &] (* Geoffrey Critzer, Nov 07 2015 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Oct 03 2008
EXTENSIONS
More terms from R. J. Mathar, Oct 04 2008
STATUS
approved