OFFSET
1,1
COMMENTS
3^(p-1)-2^(p+1) can be written as (3^((p-1)/2)-2^((p+1)/2))*(3^((p-1)/2)+2^((p+1)/2)). Since 3^((p-1)/2)-2^((p+1)/2) > 1 for p > 5, these numbers are all composite after 17 = (3^2-2^3)*(3^2+2^3).
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..200
MATHEMATICA
Table[3^(Prime[n] - 1) - 2^(Prime[n] + 1), {n, 3, 100}]
PROG
(Magma) [3^(p-1)-2^(p+1): p in PrimesInInterval(4, 100)];
CROSSREFS
KEYWORD
nonn,easy,less
AUTHOR
Vincenzo Librandi, Jun 17 2014
STATUS
approved