Omniprimorial

A(1) = 0

A(2) = 0 + 2 = 2

A(3) = 0 + 2 * 3 = 6

A(4) = 0 + 2 * 3 ^ 5 = 7776

A(5) = 0 + 2 * 3 ^ 5 ^^ 7 = 7776^^7

etc.