a(n) = n * LegendreP(n, 3).

Terms

a(0) =0a(1) =3a(2) =26a(3) =189a(4) =1284a(5) =8415a(6) =53934a(7) =340473a(8) =2125832a(9) =13163067a(10) =80974530a(11) =495513909a(12) =3019151628a(13) =18329137047a(14) =110933875542a(15) =669635727345