Centered octahedral numbers (crystal ball sequence for cubic lattice).

Terms

a(0) =1a(1) =7a(2) =25a(3) =63a(4) =129a(5) =231a(6) =377a(7) =575a(8) =833a(9) =1159a(10) =1561a(11) =2047a(12) =2625a(13) =3303a(14) =4089a(15) =4991a(16) =6017a(17) =7175a(18) =8473a(19) =9919a(20) =11521a(21) =13287a(22) =15225a(23) =17343a(24) =19649a(25) =22151a(26) =24857a(27) =27775a(28) =30913a(29) =34279