a(n) = (Fibonacci(2n-1) - Fibonacci(n+1))/2.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =4a(5) =13a(6) =38a(7) =106a(8) =288a(9) =771a(10) =2046a(11) =5401a(12) =14212a(13) =37324a(14) =97904a(15) =256621a(16) =672336a(17) =1760997a(18) =4611642a(19) =12075526a(20) =31617520a(21) =82781215a(22) =216732890a(23) =567428401a(24) =1485570024a(25) =3889310328a(26) =10182407328a(27) =26657986681a(28) =69791674108