a(n) is the constant term in expansion of Product_{k=1..n} (x^prime(k) + 1 + 1/x^prime(k)).

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =5a(5) =7a(6) =17a(7) =39a(8) =95a(9) =233a(10) =561a(11) =1435a(12) =3643a(13) =9417a(14) =24973a(15) =66695a(16) =177915a(17) =475629a(18) =1293017a(19) =3517223a(20) =9636365a(21) =26676197a(22) =73848517a(23) =205382439a(24) =571628347a(25) =1588203787a(26) =4435819313a(27) =12474619295a(28) =35194448271a(29) =99782519701