OFFSET
1,2
LINKS
D. Callan, T. Mansour, Enumeration of small Wilf classes avoiding 1324 and two other 4-letter patterns, arXiv:1705.00933 [math.CO] (2017), Table 2 No 114.
Lara Pudwell, Systematic Studies in Pattern Avoidance, 2005.
Index entries for linear recurrences with constant coefficients, signature (8,-28,56,-70,56,-28,8,-1).
FORMULA
G.f.: A(x) = -{(x^9-3x^8+3x^7-4x^6+19x^5-32x^4+27x^3-18x^2+6x-1)x}/{(x-1)^8}
For n >= 4, a(n) = (5n^6 - 84n^5 + 860n^4 - 5610n^3 + 22535n^2 - 49566n + 45900)/180. - Franklin T. Adams-Watters, Sep 16 2006
MATHEMATICA
LinearRecurrence[{8, -28, 56, -70, 56, -28, 8, -1}, {1, 2, 6, 21, 74, 237, 668, 1667, 3750, 7743}, 30] (* Harvey P. Dale, Mar 30 2024 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Lara Pudwell, Feb 26 2006
STATUS
approved