a(n) = (1/4)*Sum_{j=1..n} 2^prime(j).

Terms

a(0) =0a(1) =1a(2) =3a(3) =11a(4) =43a(5) =555a(6) =2603a(7) =35371a(8) =166443a(9) =2263595a(10) =136481323a(11) =673352235a(12) =35033090603a(13) =584788904491