Number of length-4 0..n arrays with no following elements larger than the first repeated value.

Terms

a(0) =12a(1) =62a(2) =204a(3) =515a(4) =1096a(5) =2072a(6) =3592a(7) =5829a(8) =8980a(9) =13266a(10) =18932a(11) =26247a(12) =35504a(13) =47020a(14) =61136a(15) =78217a(16) =98652a(17) =122854a(18) =151260a(19) =184331a(20) =222552a(21) =266432a(22) =316504a(23) =373325a(24) =437476a(25) =509562a(26) =590212a(27) =680079a(28) =779840a(29) =890196