A331776(n)/4.

Terms

a(0) =1a(1) =14a(2) =52a(3) =124a(4) =254a(5) =446a(6) =746a(7) =1164a(8) =1742a(9) =2486a(10) =3494a(11) =4732a(12) =6340a(13) =8282a(14) =10622a(15) =13400a(16) =16808a(17) =20726a(18) =25436a(19) =30808a(20) =36974a(21) =43946a(22) =52074a(23) =61104a(24) =71400a(25) =82838a(26) =95652a(27) =109752a(28) =125694a(29) =142978