OFFSET
1,2
COMMENTS
LINKS
Index entries for linear recurrences with constant coefficients, signature (3,-2,-2,3,-1).
FORMULA
a(n) = 3*a(n-1)-2*a(n-2)-2*a(n-3)+3*a(n-4)-a(n-5).
a(n) = (-1+(-1)^n-2*n^2+4*n^3)/8. G.f.: x^2*(3+2*x+x^2)/((1-x)^4*(1+x)). [Colin Barker, May 06 2012]
EXAMPLE
For n=2, the 3 triples (w,x,y) for which 2w<x+y are (1,1,2), (1,2,1), (1,2,2). The 3 triples for which 2w>x+y are (2,1,1), (2,1,2), (2,2,1).
MATHEMATICA
(See the program at A211802.)
LinearRecurrence[{3, -2, -2, 3, -1}, {0, 3, 11, 28, 56}, 50] (* Harvey P. Dale, Aug 10 2019 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Apr 22 2012
STATUS
approved