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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A059947 Number of 6-block bicoverings of an n-set. 3
0, 0, 0, 3, 256, 7255, 149660, 2681063, 44659776, 714287535, 11154475420, 171673613023, 2618246526896, 39701554817015, 599773397512380, 9038881598035383, 136004367641775616, 2044264589908169695, 30705868769902628540, 461006369270166660143, 6919274132365824549936 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

REFERENCES

I. P. Goulden and D. M.Jackson, Combinatorial Enumeration, John Wiley and Sons, N.Y., 1983.

LINKS

Georg Fischer, Table of n, a(n) for n = 1..500

Index entries for linear recurrences with constant coefficients, signature (48,-932,9550,-56319,194762,-382908,387000,-151200).

FORMULA

a(n) = (1/6!)*(15^n - 6*10^n - 15*7^n + 30*6^n + 60*4^n - 50*3^n - 180*2^n + 240).

E.g.f.: exp(-x-1/2*x^2*(exp(y)-1)) * Sum_{i>=0} x^i/i!*exp(binomial(i, 2)*y), for m-block bicoverings of an n-set.

G.f.: x^4*(16800*x^4-11362*x^3+2237*x^2-112*x-3) / ((1-x)*(2*x-1)*(3*x-1)*(4*x-1)*(6*x-1)*(7*x-1)*(10*x-1)*(15*x-1)). [Colin Barker, Jan 11 2013; corrected by Georg Fischer, May 18 2019]

MATHEMATICA

CoefficientList[Series[x^4*(16800*x^4-11362*x^3+2237*x^2-112*x-3) / ((1-x)*(2*x-1)*(3*x-1)*(4*x-1)*(6*x-1)*(7*x-1)*(10*x-1)*(15*x-1)), {x, 0, 21}], x] (* Georg Fischer, May 18 2019 *)

PROG

(PARI) a(n)=(1/6!)*(15^n-6*10^n-15*7^n+30*6^n+60*4^n-50*3^n-180*2^n+240) \\ Georg Fischer, May 18 2019

CROSSREFS

Column k=6 of A059443.

Cf. A002718.

Sequence in context: A320023 A045824 A027860 * A203495 A051490 A232545

Adjacent sequences:  A059944 A059945 A059946 * A059948 A059949 A059950

KEYWORD

easy,nonn

AUTHOR

Vladeta Jovovic, Feb 14 2001

EXTENSIONS

More terms from Colin Barker, Jan 11 2013

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.

License Agreements, Terms of Use, Privacy Policy. .

Last modified October 18 08:58 EDT 2021. Contains 348067 sequences. (Running on oeis4.)