Sum of the principal diagonals of a 2n X 2n square spiral.

Terms

a(0) =0a(1) =10a(2) =56a(3) =170a(4) =384a(5) =730a(6) =1240a(7) =1946a(8) =2880a(9) =4074a(10) =5560a(11) =7370a(12) =9536a(13) =12090a(14) =15064a(15) =18490a(16) =22400a(17) =26826a(18) =31800a(19) =37354a(20) =43520a(21) =50330a(22) =57816a(23) =66010a(24) =74944a(25) =84650a(26) =95160a(27) =106506a(28) =118720a(29) =131834