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A357288
a(n) = (1/4)*A357287(n).
1
0, 0, 0, 0, 0, 0, 1, 2, 5, 12, 23, 42, 85, 144, 251, 454, 753, 1244, 2183, 3506, 5725, 9736, 15539, 24926, 41993, 66228, 105823, 176138, 277173, 439648, 729099, 1141430, 1807713, 2981900, 4663991, 7361890, 12124173, 18918072, 29840739, 49020942
OFFSET
0,8
FORMULA
a(n) = 2*a(n-1) + a(n-2) - 6*a(n-4) - 4*a(n-5) + 16*a(n-6) - 8*a(n-7).
G.f.: x^6/((-1 + x)^2 (-1 + 2 x^2) (-1 + 4 x^3)).
MATHEMATICA
s[n_] := s[n] = Select[Subsets[Range[n]], Length[#] >= 3 &];
a[n_] := Select[s[n], #[[1]] + #[[2]] + #[[3]] == #[[-1]] &]
(1/4)*Table[Length[a[n]], {n, 0, 15}]
CROSSREFS
Cf. A357287.
Sequence in context: A115520 A116735 A096376 * A326510 A112287 A127787
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Oct 02 2022
STATUS
approved