Numbers k such that (-k!! + (k+1)!! - 1)/2 is prime.

Terms

a(0) =3a(1) =4a(2) =7a(3) =9a(4) =17a(5) =25a(6) =28a(7) =55a(8) =73a(9) =130a(10) =172a(11) =327a(12) =601a(13) =1201a(14) =2329a(15) =5434a(16) =8807a(17) =14074a(18) =16023