This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A059950 Number of 9-block bicoverings of an n-set. 5
 0, 0, 0, 0, 0, 15, 8456, 954213, 66253552, 3622342095, 172672602432, 7557346901841, 312733696544984, 12456923582109435, 483124650731622328, 18383758048494864909, 689931203330381971296, 25630900118611348761735, 945025181750878420241744, 34647077709586498046291817 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,6 REFERENCES I. P. Goulden and D. M. Jackson, Combinatorial Enumeration, John Wiley and Sons, N.Y., 1983. LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..200 FORMULA a(n)=(1/9!)*(36^n -9*28^n -36*22^n +72*21^n +252*16^n -336*15^n +378*12^n -1512*11^n +1260*10^n -1890*8^n +5040*7^n -4536*6^n +7560*5^n -8820*4^n -11256*3^n +28728*2^n -19152). E.g.f. for m-block bicoverings of an n-set is exp(-x-1/2*x^2*(exp(y)-1))*Sum_{i=0..inf} x^i/i!*exp(binomial(i, 2)*y). G.f.: x^6*(69766476595200*x^11 -73112128911360*x^10 +31807557729984*x^9 -7437208397056*x^8 +993276127572*x^7 -70229555428*x^6 +1198328731*x^5 +199609307*x^4 -16366808*x^3 +505224*x^2 -5351*x -15) / ((x -1)*(2*x -1)*(3*x -1)*(4*x -1)*(5*x -1)*(6*x -1)*(7*x -1)*(8*x -1)*(10*x -1)*(11*x -1)*(12*x -1)*(15*x -1)*(16*x -1)*(21*x -1)*(22*x -1)*(28*x -1)*(36*x -1)). - Colin Barker, Jul 09 2013 CROSSREFS Cf. A002718, A059443, A003462, A059945-A059949, A059951. Sequence in context: A205304 A206295 A074488 * A198979 A249967 A308156 Adjacent sequences:  A059947 A059948 A059949 * A059951 A059952 A059953 KEYWORD easy,nonn AUTHOR Vladeta Jovovic, Feb 14 2001 STATUS approved

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.

Last modified October 20 07:23 EDT 2019. Contains 328252 sequences. (Running on oeis4.)