Create FastTn

an odd number n = p1 + p2 + p3, p1 <= p2 <= p3, p1, p2, p3 all are primes,
define T(n) as number of 3-tuples (p1, p2, p3),
and G(n) is defined as number of prime Pairs (p1, p2) with n = p1 + p2, p1 <= p2