|
|
A151577
|
|
Number of permutations of 1..n arranged in a circle with exactly 4 adjacent element pairs in decreasing order.
|
|
3
|
|
|
0, 5, 156, 2114, 19328, 140571, 882340, 5007112, 26441856, 132439905, 637468300, 2976161790, 13569454592, 60725449335, 267757190100, 1166662948900, 5034645823680, 21556696454685, 91704869986620, 388044105102650, 1634678955350400, 6860481786528275, 28700914012807556
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
4,2
|
|
LINKS
|
|
|
FORMULA
|
a(n) = n*(4^(n-1) - n*3^(n-1) + binomial(n,2)*2^(n-1) - binomial(n,3)). (End)
|
|
PROG
|
(PARI) a(n) = {n*(4^(n-1) - n*3^(n-1) + binomial(n, 2)*2^(n-1) - binomial(n, 3))} \\ Andrew Howroyd, May 05 2020
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|