Alternating sum of centered octagonal pyramidal numbers.

Terms

a(0) =0a(1) =-1a(2) =9a(3) =-26a(4) =58a(5) =-107a(6) =179a(7) =-276a(8) =404a(9) =-565a(10) =765a(11) =-1006a(12) =1294a(13) =-1631a(14) =2023a(15) =-2472a(16) =2984a(17) =-3561a(18) =4209a(19) =-4930a(20) =5730a(21) =-6611a(22) =7579a(23) =-8636a(24) =9788a(25) =-11037a(26) =12389a(27) =-13846a(28) =15414a(29) =-17095