A156790(n+1)-4*A156790(n).

Terms

a(0) =1a(1) =4a(2) =9a(3) =19a(4) =38a(5) =69a(6) =134a(7) =289a(8) =520a(9) =1076a(10) =2134a(11) =4098a(12) =8376a(13) =16559a(14) =33020a(15) =66114a(16) =132119a(17) =263585a(18) =525765a(19) =1050309a(20) =2097946a(21) =4199226a(22) =8394235a(23) =16785959