a(n) = (2n+1)!! mod (2n)!! where k!! = A006882(k).

A306184

a(n) = (2n+1)!! mod (2n)!! where k!! = A006882(k).

Terms

    a(0) =1a(1) =7a(2) =9a(3) =177a(4) =2715a(5) =42975a(6) =91665a(7) =3493665a(8) =97345395a(9) =2601636975a(10) =70985324025a(11) =57891366225

External references