A357287 a(n) = number of subsets S of {1,2,...,n} having more than 2 elements such that (sum of least three elements of S) = max(S).

0, 0, 0, 0, 0, 0, 4, 8, 20, 48, 92, 168, 340, 576, 1004, 1816, 3012, 4976, 8732, 14024, 22900, 38944, 62156, 99704, 167972, 264912, 423292, 704552, 1108692, 1758592, 2916396, 4565720, 7230852, 11927600, 18655964, 29447560, 48496692, 75672288, 119362956

Offset

0,7

Links

Table of n, a(n) for n=0..38.

Index entries for linear recurrences with constant coefficients, signature (2, 1, 0, -6, -4, 16, -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.: (4 x^6)/((-1 + x)^2 (-1 + 2 x^2) (-1 + 4 x^3)).

Example

The 4 relevant subsets of {1,2,3,4,5,6} are
{1, 2, 3, 6}, {1, 2, 3, 4, 6}, {1, 2, 3, 5, 6}, and {1, 2, 3, 4, 5, 6}.

Mathematica

s[n_] := s[n] = Select[Subsets[Range[n]], Length[#] >= 3 &];
a[n_] := Select[s[n], #[[1]] + #[[2]] + #[[3]] == #[[-1]] &]
Table[Length[a[n]], {n, 0, 15}]

Crossrefs

Cf. A357285, A357288, A357289.

Sequence in context: A009916 A203167 A123861 * A371596 A115099 A060919

Adjacent sequences: A357284 A357285 A357286 * A357288 A357289 A357290

Keyword

nonn,easy

Author

Clark Kimberling, Oct 02 2022

Status

approved