a(n) = 3*a(n-1) - 3*a(n-2) + 2*a(n-3), with a(0) = a(1) = -1 and a(2) = 3.

Terms

a(0) =-1a(1) =-1a(2) =3a(3) =10a(4) =19a(5) =33a(6) =62a(7) =125a(8) =255a(9) =514a(10) =1027a(11) =2049a(12) =4094a(13) =8189a(14) =16383a(15) =32770a(16) =65539a(17) =131073a(18) =262142a(19) =524285a(20) =1048575a(21) =2097154a(22) =4194307a(23) =8388609a(24) =16777214a(25) =33554429a(26) =67108863a(27) =134217730a(28) =268435459a(29) =536870913