A190919 - OEIS

%I #5 Mar 31 2012 12:36:20

%S 1,10,109,1277,15743,201562,2655555,35772051,490468025,6822301766,

%T 96037376333,1365601216463,19585937393943,283004879815278,

%U 4115869618377271,60201892791282135,885032788096094565

%N Number of permutations of n copies of 1..4 introduced in order 1..4 with no element equal to another within a distance of 2

%H R. H. Hardin, <a href="/A190919/b190919.txt">Table of n, a(n) for n = 1..121</a>

%e All solutions for n=2

%e ..1....1....1....1....1....1....1....1....1....1

%e ..2....2....2....2....2....2....2....2....2....2

%e ..3....3....3....3....3....3....3....3....3....3

%e ..4....4....4....4....1....4....4....4....1....4

%e ..2....2....2....1....4....1....1....1....4....2

%e ..1....3....1....3....2....2....2....3....3....3

%e ..3....4....4....2....3....4....3....4....2....1

%e ..4....1....3....4....4....3....4....2....4....4

%K nonn

%O 1,2

%A _R. H. Hardin_ May 23 2011