OFFSET
0,5
LINKS
Index entries for linear recurrences with constant coefficients, signature (4,-3,-6,10,-4).
FORMULA
a(n) = 4*a(n-1) - 3*a(n-2) - 6*a(n-3) + 10*a(n-4) - 4*a(n-5).
G.f.: (2 x^4)/((-1 + x)^2 (1 - 2 x - 2 x^2 + 4 x^3)).
EXAMPLE
The 2 relevant subsets of {1,2,3,4} and {1,2,4} and {1,2,3,4}.
MATHEMATICA
s[n_] := s[n] = Select[Subsets[Range[n]], Length[#] >= 2 &]; (* note size >=2 *)
a[n_] := Select[s[n], #[[2]] + #[[1]] < #[[-1]] &]
Table[Length[a[n]], {n, 0, 18}]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Sep 27 2022
STATUS
approved