a(n) = A111877(n+1)/5.

Terms

a(0) =1a(1) =7a(2) =21a(3) =231a(4) =3003a(5) =3003a(6) =51051a(7) =969969a(8) =969969a(9) =22309287a(10) =111546435a(11) =334639305a(12) =9704539845a(13) =300840735195a(14) =300840735195a(15) =300840735195