A055485 Number of unlabeled 3-element intersecting families (with distinct sets) of an n-element set.

4, 19, 61, 157, 353, 717, 1355, 2412, 4094, 6676, 10524, 16108, 24036, 35063, 50135, 70409, 97295, 132485, 178011, 236268, 310086, 402768, 518158, 660692, 835486, 1048379, 1306039, 1616025, 1986887, 2428245, 2950913, 3566968, 4289896

Offset

3,1

Links

G. C. Greubel, Table of n, a(n) for n = 3..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 (3,1,-9,0,12,7,-15,-16,16,15,-7,-12,0,9,-1,-3,1).

Formula

G.f.: -x^3*(x^8+x^7-3*x^6-x^5+x^4+3*x^3-x^2-3*x-4)/((x^3-1)^2*(x^2-1)^2*(x-1)^4).

Mathematica

Rest[Rest[Rest[CoefficientList[Series[-x^3*(x^8 + x^7 - 3*x^6 - x^5 + x^4 + 3*x^3 - x^2 - 3*x - 4)/((x^3 - 1)^2*(x^2 - 1)^2*(x - 1)^4), {x, 0, 50}], x]]]] (* G. C. Greubel, Oct 06 2017 *)
LinearRecurrence[{3, 1, -9, 0, 12, 7, -15, -16, 16, 15, -7, -12, 0, 9, -1, -3, 1}, {4, 19, 61, 157, 353, 717, 1355, 2412, 4094, 6676, 10524, 16108, 24036, 35063, 50135, 70409, 97295}, 33] (* Vincenzo Librandi, Oct 07 2017 *)

Prog

(PARI) x='x+O('x^50); Vec(-x^3*(x^8+x^7-3*x^6-x^5+x^4+3*x^3-x^2-3*x-4)/((x^3-1)^2*(x^2-1)^2*(x-1)^4)) \\ G. C. Greubel, Oct 06 2017

Crossrefs

Cf. A051180 (labeled case), A005783.

Sequence in context: A134507 A098813 A212039 * A000306 A100185 A357251

Adjacent sequences: A055482 A055483 A055484 * A055486 A055487 A055488

Keyword

nonn

Author

Vladeta Jovovic, Goran Kilibarda, Jul 03 2000

Extensions

More terms from James A. Sellers, Jul 04 2000

Status

approved