a(n) = 6 * A015518(n).

Terms

a(0) =0a(1) =6a(2) =12a(3) =42a(4) =120a(5) =366a(6) =1092a(7) =3282a(8) =9840a(9) =29526a(10) =88572a(11) =265722a(12) =797160a(13) =2391486a(14) =7174452a(15) =21523362a(16) =64570080a(17) =193710246a(18) =581130732a(19) =1743392202a(20) =5230176600a(21) =15690529806a(22) =47071589412a(23) =141214768242a(24) =423644304720