A177316 Number of permutations of n copies of 1..4 with all adjacent differences <= 1 in absolute value.

2, 26, 506, 11482, 284002, 7426610, 201922730, 5650739930, 161686253810, 4708709084026, 139111173397066, 4159013698117618, 125595645802182818, 3825428523179727266, 117382025506323434506, 3625185567639373456090