OFFSET
0,4
COMMENTS
a(n) is the number of 231-avoiding permutations of length n that have order 1 or 3.
LINKS
Amanda Burcroff and Colin Defant, Pattern-Avoiding Permutation Powers, arXiv:1907.09451 [math.CO], 2019.
Index entries for linear recurrences with constant coefficients, signature (1,0,3,0,1).
FORMULA
G.f.: (1-x+x^2)*(1+x+x^2)/(1-x-3*x^3-x^5).
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Colin Defant, Jul 23 2019
STATUS
approved