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

Terms

a(0) =2a(1) =3a(2) =4a(3) =5a(4) =28a(5) =35a(6) =61a(7) =75a(8) =218a(9) =267a(10) =395a(11) =844a(12) =1509a(13) =2122a(14) =4157a(15) =14707a(16) =19996a(17) =21483a(18) =22450