Second elementary symmetric function of the first n terms of (1,2,3,5,8,...).

Terms

a(0) =2a(1) =11a(2) =41a(3) =129a(4) =376a(5) =1048a(6) =2850a(7) =7635a(8) =20273a(9) =53537a(10) =140912a(11) =370128a(12) =970978a(13) =2545243a(14) =6668697a(15) =17467233a(16) =45743336a(17) =119779496a(18) =313622210a(19) =821130915a(20) =2149841377a(21) =5628507841a(22) =14735867616a(23) =38579395104a(24) =101002803266a(25) =264429800363