a(n) = Sum_{k=1..n} 2^prime(k).

Terms

a(0) =0a(1) =4a(2) =12a(3) =44a(4) =172a(5) =2220a(6) =10412a(7) =141484a(8) =665772a(9) =9054380a(10) =545925292a(11) =2693408940a(12) =140132362412