A055484 Number of unlabeled 3-element intersecting families (with not necessarily distinct sets) of an n-element set.

1, 4, 14, 39, 96, 213, 437, 837, 1520, 2632, 4380, 7040, 10979, 16668, 24716, 35879, 51104, 71549, 98625, 134025, 179782, 238292, 312386, 405368, 521083, 663968, 839140, 1052439, 1310534, 1620985, 1992343, 2434229, 2957458, 3574108

Offset

1,2

Links

G. C. Greubel, Table of n, a(n) for n = 1..1000

V. Jovovic, G. Kilibarda, On the number of Boolean functions in the Post classes F^{mu}_8, (in Russian), Diskretnaya Matematika, 11 (1999), no. 4, 127-138.

V. Jovovic, G. Kilibarda, On the number of Boolean functions in the Post classes F^{mu}_8, (English translation), Discrete Mathematics and Applications, 9, (1999), no. 6.

Index entries for linear recurrences with constant coefficients, signature (4, -4, -2, 2, 4, 3, -12, 3, 4, 2, -2, -4, 4, -1).

Formula

G.f.: -x*(x^3-x^2-1)*(x^6+x^4+2*x^3+x^2+1)/((x^3-1)^2*(x^2-1)^2*(x-1)^4).

Mathematica

Rest[CoefficientList[Series[-x*(x^3 - x^2 - 1)*(x^6 + x^4 + 2*x^3 + x^2 + 1)/((x^3 - 1)^2*(x^2 - 1)^2*(x - 1)^4), {x, 0, 50}], x]] (* G. C. Greubel, Oct 06 2017 *)

Prog

(PARI) x='x+O('x^50); Vec(-x*(x^3-x^2-1)*(x^6+x^4+2*x^3+x^2+1)/( (x^3-1)^2*(x^2-1)^2*(x-1)^4)) \\ G. C. Greubel, Oct 06 2017

Crossrefs

Cf. A053155 (labeled case), A005783, A002727, A051180.

Sequence in context: A064463 A130423 A266423 * A055279 A074083 A182819

Adjacent sequences: A055481 A055482 A055483 * A055485 A055486 A055487

Keyword

nonn

Author

Vladeta Jovovic, Goran Kilibarda, Jul 03 2000

Extensions

More terms from James A. Sellers, Jul 04 2000

Status

approved