a(n) = (n-3)*A006918(n-2)/2 for n >= 2, with a(0) = a(1) = 0.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =5a(6) =12a(7) =28a(8) =50a(9) =90a(10) =140a(11) =220a(12) =315a(13) =455a(14) =616a(15) =840a(16) =1092a(17) =1428a(18) =1800a(19) =2280a(20) =2805a(21) =3465a(22) =4180a(23) =5060a(24) =6006a(25) =7150a(26) =8372a(27) =9828a(28) =11375a(29) =13195