a(n) = 2*a(n-1) - a(n-3) + 2*a(n-4) for n>3, a(0)=1, a(1)=-1, a(2)=4, a(3)=8.

Terms

a(0) =1a(1) =-1a(2) =4a(3) =8a(4) =19a(5) =32a(6) =64a(7) =125a(8) =256a(9) =512a(10) =1027a(11) =2048a(12) =4096a(13) =8189a(14) =16384a(15) =32768a(16) =65539a(17) =131072a(18) =262144a(19) =524285a(20) =1048576a(21) =2097152a(22) =4194307a(23) =8388608a(24) =16777216a(25) =33554429a(26) =67108864a(27) =134217728a(28) =268435459a(29) =536870912