a(n) = ((2*n+1)^4+1)/2.

Terms

a(0) =1a(1) =41a(2) =313a(3) =1201a(4) =3281a(5) =7321a(6) =14281a(7) =25313a(8) =41761a(9) =65161a(10) =97241a(11) =139921a(12) =195313a(13) =265721a(14) =353641a(15) =461761a(16) =592961a(17) =750313a(18) =937081a(19) =1156721a(20) =1412881a(21) =1709401a(22) =2050313a(23) =2439841a(24) =2882401a(25) =3382601a(26) =3945241a(27) =4575313a(28) =5278001a(29) =6058681