a(n) = prime(n) * prime(2*n-1).

Terms

a(0) =4a(1) =15a(2) =55a(3) =119a(4) =253a(5) =403a(6) =697a(7) =893a(8) =1357a(9) =1943a(10) =2263a(11) =3071a(12) =3977a(13) =4429a(14) =5123a(15) =6731a(16) =8083a(17) =9089a(18) =10519a(19) =11857a(20) =13067a(21) =15089a(22) =16351a(23) =18779a(24) =22019a(25) =23533a(26) =24823a(27) =27499a(28) =29321a(29) =31301