Alternating sum of the squares of the first n Jacobsthal numbers.

Terms

a(0) =0a(1) =1a(2) =0a(3) =9a(4) =-16a(5) =105a(6) =-336a(7) =1513a(8) =-5712a(9) =23529a(10) =-92752a(11) =373737a(12) =-1489488a(13) =5968873a(14) =-23853648a(15) =95458281a(16) =-381745744a(17) =1527157737a(18) =-6108281424a(19) =24433824745a(20) =-97733900880a(21) =390938399721