Grand primorial

A(1) = 2

A(2) = 2^2 + 3^2 = 13

A(3) = 2^3 * 3^3 * 5^3 = 27000

A(4) = (2^4)^(3^4)^(5^4)^(7^4) = 16^81^625^2401

etc.