a(n) is the first Zagreb index of the Fibonacci cube Gamma(n).

Terms

a(0) =2a(1) =6a(2) =22a(3) =54a(4) =132a(5) =292a(6) =626a(7) =1290a(8) =2594a(9) =5102a(10) =9864a(11) =18792a(12) =35362a(13) =65838a(14) =121454a(15) =222246a(16) =403788a(17) =728972a(18) =1308562a(19) =2336946a(20) =4154170a(21) =7353310a(22) =12965904a(23) =22781520a(24) =39897410a(25) =69662166a(26) =121292998a(27) =210642966a(28) =364928532a(29) =630794356