A generalized Jacobsthal sequence.

Terms

a(0) =0a(1) =1a(2) =-2a(3) =-3a(4) =-10a(5) =-19a(6) =-42a(7) =-83a(8) =-170a(9) =-339a(10) =-682a(11) =-1363a(12) =-2730a(13) =-5459a(14) =-10922a(15) =-21843a(16) =-43690a(17) =-87379a(18) =-174762a(19) =-349523a(20) =-699050a(21) =-1398099a(22) =-2796202a(23) =-5592403a(24) =-11184810a(25) =-22369619a(26) =-44739242a(27) =-89478483a(28) =-178956970a(29) =-357913939