OFFSET
1,2
LINKS
D. Callan, T. Mansour, Enumeration of small Wilf classes avoiding 1324 and two other 4-letter patterns, arXiv:1705.00933 (2017), Table 2 No 21.
Lara Pudwell, Systematic Studies in Pattern Avoidance, 2005.
Index entries for linear recurrences with constant coefficients, signature (7, -21, 35, -35, 21, -7, 1).
FORMULA
G.f.: A(x) = -{x(2x^8-3x^7+x^6-9x^5+15x^4-14x^3+13x^2-5x+1)}/{(x-1)^7}
For n >= 3, a(n) = (n^6 + 45n^5 - 245n^4 - 465n^3 + 8164n^2 - 24780n + 25920)/720. - Franklin T. Adams-Watters, Sep 16 2006
a(1)=1, a(2)=2, a(3)=6, a(4)=21, a(5)=71, a(6)=208, a(7)=526, a(8)=1174, a(9)=2370, a(n)=7*a(n-1)-21*a(n-2)+35*a(n-3)-35*a(n-4)+21*a(n-5)- 7*a(n-6)+a (n-7) [From Harvey P. Dale, Aug 31 2011]
MATHEMATICA
Join[{1, 2, 6}, Table[(n^6+45n^5-245n^4-465n^3+8164n^2-24780n+25920)/ 720, {n, 4, 40}]] (* or *) Join[{1, 2}, LinearRecurrence[ {7, -21, 35, -35, 21, -7, 1}, {6, 21, 71, 208, 526, 1174, 2370}, 40]] (* Harvey P. Dale, Aug 31 2011 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Lara Pudwell, Feb 26 2006
STATUS
approved