A177291 - OEIS

%I #17 May 16 2020 01:33:21

%S 1,1,20,92,506,2288,10010,41618,168284,664958,2584442,9916688,

%T 37679618,142079906,532572428,1987037318,7386724082,27381500624,

%U 101272019258,373902595130,1378571667644,5077289249390,18683930010890,68709775705328,252549056389394,927895845621746

%N Number of permutations of 3 copies of 1..n with all adjacent differences <= 1 in absolute value.

%C a(n) = (3n)!/6^n = A014606(n) for n<=2.

%H Andrew Howroyd, <a href="/A177291/b177291.txt">Table of n, a(n) for n = 0..200</a>

%Y Column k=3 of A331562.

%Y Cf. A014606.

%K nonn

%O 0,3

%A _R. H. Hardin_, May 06 2010

%E a(0)=1 prepended by _Alois P. Heinz_, Jan 21 2020

%E a(19)-a(20) from _Alois P. Heinz_, Jan 22 2020

%E Terms a(21) and beyond from _Andrew Howroyd_, May 14 2020