COMPOSE primes with primes.

Terms

a(0) =4a(1) =18a(2) =86a(3) =393a(4) =1790a(5) =7918a(6) =34047a(7) =142442a(8) =582768a(9) =2344913a(10) =9330350a(11) =36842164a(12) =144611963a(13) =564509442a(14) =2191142528a(15) =8453688007a(16) =32411106626a(17) =123493645782a(18) =467831766283