a(n) = (2*n-3-(-1)^n)*(22*n^2-21*n+5*n*(-1)^n)/96.

Terms

a(0) =0a(1) =0a(2) =5a(3) =12a(4) =35a(5) =58a(6) =112a(7) =160a(8) =258a(9) =340a(10) =495a(11) =620a(12) =845a(13) =1022a(14) =1330a(15) =1568a(16) =1972a(17) =2280a(18) =2793a(19) =3180a(20) =3815a(21) =4290a(22) =5060a(23) =5632a(24) =6550a(25) =7228a(26) =8307a(27) =9100a(28) =10353a(29) =11270