OFFSET
0,3
LINKS
Colin Barker, Table of n, a(n) for n = 0..1000
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 24.
Index entries for linear recurrences with constant coefficients, signature (7,-21,35,-35,21,-7,1).
FORMULA
From Colin Barker, Nov 10 2017: (Start)
G.f.: (1 - 6*x + 16*x^2 - 22*x^3 + 21*x^4 - 6*x^5 + 2*x^6) / (1 - x)^7.
a(n) = (1/120)*(120 - 40*n + 44*n^2 - 15*n^3 + 15*n^4 - 5*n^5 + n^6).
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) for n>6.
(End)
MAPLE
cn := [1, -6, 16, -22, 21, -6, 2] ;
p := add(cn[i]*x^(i-1), i=1..nops(cn)) ;
q := (1-x)^7 ;
taylor(p/q, x=0, 40) ;
gfun[seriestolist](%) ;
PROG
(PARI) Vec((1 - 6*x + 16*x^2 - 22*x^3 + 21*x^4 - 6*x^5 + 2*x^6) / (1 - x)^7 + O(x^40)) \\ Colin Barker, Nov 10 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
R. J. Mathar, Nov 07 2017
STATUS
approved