a(n) = 3*a(n-1) - a(n-3) for n>2, with a(0)=1, a(1)=-1, a(2)=0.

Terms

a(0) =1a(1) =-1a(2) =0a(3) =-1a(4) =-2a(5) =-6a(6) =-17a(7) =-49a(8) =-141a(9) =-406a(10) =-1169a(11) =-3366a(12) =-9692a(13) =-27907a(14) =-80355a(15) =-231373a(16) =-666212a(17) =-1918281a(18) =-5523470a(19) =-15904198a(20) =-45794313a(21) =-131859469a(22) =-379674209a(23) =-1093228314a(24) =-3147825473a(25) =-9063802210a(26) =-26098178316a(27) =-75146709475a(28) =-216376326215a(29) =-623030800329