a(n) = prime(n) * 4^prime(n) - 1.A100689a(n) = prime(n) * 4^prime(n) - 1.Terms a(0) =31a(1) =191a(2) =5119a(3) =114687a(4) =46137343a(5) =872415231a(6) =292057776127External referencesoeis: A100689