Alternating sum of octagonal pyramidal numbers.

Terms

a(0) =0a(1) =-1a(2) =8a(3) =-22a(4) =48a(5) =-87a(6) =144a(7) =-220a(8) =320a(9) =-445a(10) =600a(11) =-786a(12) =1008a(13) =-1267a(14) =1568a(15) =-1912a(16) =2304a(17) =-2745a(18) =3240a(19) =-3790a(20) =4400a(21) =-5071a(22) =5808a(23) =-6612a(24) =7488a(25) =-8437a(26) =9464a(27) =-10570a(28) =11760a(29) =-13035