OFFSET
1,2
COMMENTS
Mp is prime iff 3^(2^(p(n)-1)-1) is congruent to (-1) Mod Mp. Thus M7 = 127 is prime because 3^63 Mod 127 = 126 (=127-1) while M11 = 2047 is composite because 3^1023 Mod 2047 <> 2046.
LINKS
Dennis Martin, Table of n, a(n) for n = 1..100
FORMULA
a(n) = 3^(2^(p(n)-1)-1) Mod 2^p(n)-1
EXAMPLE
a(5) = 3^(2^(11-1)-1) Mod 2^11-1 = 3^1023 Mod 2047 = 1565
CROSSREFS
KEYWORD
nonn
AUTHOR
Dennis Martin (dennis.martin(AT)dptechnology.com), Jul 13 2007, Jul 20 2007
STATUS
approved