Number of base 4 circular n-digit numbers with adjacent digits differing by 1 or less.

Terms

a(0) =1a(1) =4a(2) =10a(3) =22a(4) =54a(5) =134a(6) =340a(7) =872a(8) =2254a(9) =5854a(10) =15250a(11) =39802a(12) =104004a(13) =271964a(14) =711490a(15) =1861862a(16) =4873054a(17) =12755614a(18) =33391060a(19) =87413152a(20) =228841254a(21) =599099054a(22) =1568437210a(23) =4106182322a(24) =10750060804a(25) =28143920884a(26) =73681573690a(27) =192900592822a(28) =505019869254