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

Terms

a(0) =1a(1) =2a(2) =-5a(3) =-1a(4) =-11a(5) =-13a(6) =-35a(7) =-61a(8) =-131a(9) =-253a(10) =-515a(11) =-1021a(12) =-2051a(13) =-4093a(14) =-8195a(15) =-16381a(16) =-32771a(17) =-65533a(18) =-131075a(19) =-262141a(20) =-524291a(21) =-1048573a(22) =-2097155a(23) =-4194301a(24) =-8388611a(25) =-16777213a(26) =-33554435a(27) =-67108861a(28) =-134217731a(29) =-268435453