Number of length-4 0..n arrays with no repeated value equal to the previous repeated value.

Terms

a(0) =10a(1) =66a(2) =228a(3) =580a(4) =1230a(5) =2310a(6) =3976a(7) =6408a(8) =9810a(9) =14410a(10) =20460a(11) =28236a(12) =38038a(13) =50190a(14) =65040a(15) =82960a(16) =104346a(17) =129618a(18) =159220a(19) =193620a(20) =233310a(21) =278806a(22) =330648a(23) =389400a(24) =455650a(25) =530010a(26) =613116a(27) =705628a(28) =808230a(29) =921630