OFFSET
1,1
COMMENTS
Since each Mersenne prime is congruent to -1 (mod 4), it is easy to see that a(n) == 1 (mod 4). - Timothy L. Tiffin, Jul 07 2021
LINKS
T. D. Noe, Table of n, a(n) for n = 1..90
G. L. Honaker, Jr. and Chris Caldwell, Prime Curios! 21
Googology Wiki,Largest known squarefree semiprime
EXAMPLE
a(1) = 3*7 = 21, a(2) = 3*31 = 93, a(3) = 7*31 = 217, ... - Timothy L. Tiffin, Jul 07 2021
MATHEMATICA
Mp = 2^{2, 3, 5, 7, 13, 17, 19, 31, 61} - 1; Take[ Union[ Times @@@ Subsets[ Mp, {2}]], 25] (* Robert G. Wilson v, Sep 25 2008 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
G. L. Honaker, Jr., Sep 22 2008
EXTENSIONS
More terms from Robert G. Wilson v, Sep 25 2008
More terms from T. D. Noe, Sep 25 2008
STATUS
approved