a(0) = 4, a(n) = 2*a(n-1) + (-1)^n.

Terms

a(0) =4a(1) =7a(2) =15a(3) =29a(4) =59a(5) =117a(6) =235a(7) =469a(8) =939a(9) =1877a(10) =3755a(11) =7509a(12) =15019a(13) =30037a(14) =60075a(15) =120149a(16) =240299a(17) =480597a(18) =961195a(19) =1922389a(20) =3844779a(21) =7689557a(22) =15379115a(23) =30758229a(24) =61516459a(25) =123032917a(26) =246065835a(27) =492131669a(28) =984263339a(29) =1968526677