Surround numbers of an n X 2 rectangle when n is odd.

Terms

a(0) =83a(1) =361a(2) =951a(3) =1997a(4) =3667a(5) =6153a(6) =9671a(7) =14461a(8) =20787a(9) =28937a(10) =39223a(11) =51981a(12) =67571a(13) =86377a(14) =108807a(15) =135293a(16) =166291a(17) =202281a(18) =243767a(19) =291277a(20) =345363a(21) =406601a(22) =475591a(23) =552957a(24) =639347a(25) =735433a(26) =841911a(27) =959501a(28) =1088947a(29) =1231017