a(n) = Sum_{m=0..floor((n-1)/2)} prime((n-m)(n-m-1)/2+m+1).

Terms

a(0) =2a(1) =3a(2) =12a(3) =28a(4) =63a(5) =113a(6) =208a(7) =296a(8) =473a(9) =657a(10) =946a(11) =1236a(12) =1661a(13) =2071a(14) =2688a(15) =3228a(16) =4059a(17) =4811a(18) =5898a(19) =6858a(20) =8209a(21) =9433a(22) =11116a(23) =12572a(24) =14637a(25) =16395a(26) =18872a(27) =21046a(28) =23935a(29) =26405