The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.



Please make a donation to keep the OEIS running. We are now in our 56th year. In the past year we added 10000 new sequences and reached almost 9000 citations (which often say "discovered thanks to the OEIS").
Other ways to donate

(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A055780 Number of symmetric types of (3,2n)-hypergraphs under action of complementing group C(3,2). 1


%S 1,7,14,35,57,98,140,210,281,385,490,637,785,980,1176,1428,1681,1995,

%T 2310,2695,3081,3542,4004,4550,5097,5733,6370,7105,7841,8680,9520,

%U 10472,11425,12495,13566,14763,15961,17290,18620,20090,21561,23177,24794,26565

%N Number of symmetric types of (3,2n)-hypergraphs under action of complementing group C(3,2).

%C The first g.f. gives a 0 between each two terms of the sequence - _Colin Barker_, Jul 12 2013

%H Harvey P. Dale, <a href="/A055780/b055780.txt">Table of n, a(n) for n = 0..1000</a>

%H <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (2,0,-2,2,-2,0,2,-1).

%F G.f.: -(x^8-9*x^6-5*x^2-1)/(1-x^2)^2/(1-x^4)/(1-x^8).

%F G.f.: -(x^4-9*x^3-5*x-1) / ((x-1)^4*(x+1)^2*(x^2+1)). - _Colin Barker_, Jul 12 2013

%e There are 7 symmetric (3,2)-hypergraphs under action of complementing group C(3,2): {{1,2},{1,2,3}}, {{1,3},{1,2,3}}, {{1,2},{1,3}}, {{2,3},{1,2,3}}, {{1,2},{2,3}}, {{1,3},{2,3}}, {{1},{2,3}}.

%p gf := -(x^8-9*x^6-5*x^2-1)/(1-x^2)^2/(1-x^4)/(1-x^8): s := series(gf, x, 200): for i from 0 to 200 by 2 do printf(`%d,`,coeff(s, x, i)) od:

%t LinearRecurrence[{2,0,-2,2,-2,0,2,-1},{1,7,14,35,57,98,140,210},50] (* _Harvey P. Dale_, May 15 2020 *)

%K nonn,easy

%O 0,2

%A _Vladeta Jovovic_, Jul 13 2000

%E More terms from _James A. Sellers_, Jul 13 2000

%E More terms from _Colin Barker_, Jul 12 2013

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified November 25 20:53 EST 2020. Contains 338627 sequences. (Running on oeis4.)