a(0) = a(1) = 1; a(n+2) = 2*a(n+1) + 2*a(n).

Terms

a(0) =1a(1) =1a(2) =4a(3) =10a(4) =28a(5) =76a(6) =208a(7) =568a(8) =1552a(9) =4240a(10) =11584a(11) =31648a(12) =86464a(13) =236224a(14) =645376a(15) =1763200a(16) =4817152a(17) =13160704a(18) =35955712a(19) =98232832a(20) =268377088a(21) =733219840a(22) =2003193856a(23) =5472827392a(24) =14952042496a(25) =40849739776a(26) =111603564544a(27) =304906608640a(28) =833020346368