a(n)=2a(n-1)+a(n-2)-2a(n-3).

Terms

a(0) =4a(1) =4a(2) =10a(3) =16a(4) =34a(5) =64a(6) =130a(7) =256a(8) =514a(9) =1024a(10) =2050a(11) =4096a(12) =8194a(13) =16384a(14) =32770a(15) =65536a(16) =131074a(17) =262144a(18) =524290a(19) =1048576a(20) =2097154a(21) =4194304a(22) =8388610a(23) =16777216a(24) =33554434a(25) =67108864a(26) =134217730a(27) =268435456a(28) =536870914a(29) =1073741824