Number of length-n 0..3 arrays with no adjacent pair x,x+1 followed at any distance by x+1,x.

A268452

Number of length-n 0..3 arrays with no adjacent pair x,x+1 followed at any distance by x+1,x.

Terms

    a(0) =4a(1) =16a(2) =61a(3) =229a(4) =852a(5) =3146a(6) =11536a(7) =42032a(8) =152254a(9) =548568a(10) =1966757a(11) =7019311a(12) =24946486a(13) =88313632a(14) =311507619a(15) =1095064315a(16) =3837407016a(17) =13407618832a(18) =46715533678a(19) =162345449332a(20) =562801287366

External references