login
This site is supported by donations to The OEIS Foundation.

 

Logo

"Email this user" was broken Aug 14 to 9am Aug 16. If you sent someone a message in this period, please send it again.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A006542 a(n) = binomial(n,3)*binomial(n-1,3)/4.
(Formerly M4707)
20
1, 10, 50, 175, 490, 1176, 2520, 4950, 9075, 15730, 26026, 41405, 63700, 95200, 138720, 197676, 276165, 379050, 512050, 681835, 896126, 1163800, 1495000, 1901250, 2395575, 2992626, 3708810, 4562425, 5573800, 6765440, 8162176, 9791320, 11682825, 13869450 (list; graph; refs; listen; history; text; internal format)
OFFSET

4,2

COMMENTS

Number of permutations of n+4 that avoid the pattern 132 and have exactly 3 descents. - Mike Zabrocki, Aug 26 2004

Kekulé numbers for certain benzenoids. - Emeric Deutsch, Jun 20 2005

a(n) = number of Dyck n-paths with exactly 4 peaks. - David Callan, Jul 03 2006

Six-dimensional figurate numbers for a hyperpyramid with pentagonal base. This corresponds to the sum(sum(sum(sum(1+sum(5*n))))) interpretation, see the Munafo webpage. - Robert Munafo, Jun 18 2009

REFERENCES

S. J. Cyvin and I. Gutman, Kekulé structures in benzenoid hydrocarbons, Lecture Notes in Chemistry, No. 46, Springer, New York, 1988 (p. 166, no. 1).

S. Mukai, An Introduction to Invariants and Moduli, Cambridge, 2003; see p. 238.

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

T. D. Noe, Table of n, a(n) for n = 4..200

P. Aluffi, Degrees of projections of rank loci, arXiv:1408.1702 [math.AG], 2014. ["After compiling the results of many explicit computations, we noticed that many of the numbers d_{n,r,S} appear in the existing literature in contexts far removed from the enumerative geometry of rank conditions; we owe this surprising (to us) observation to perusal of [Slo14]."]

Brandy Amanda Barnette, Counting Convex Sets on Products of Totally Ordered Sets, Masters Theses & Specialist Projects, Paper 1484, 2015.

V. E. Hoggatt, Jr., Letter to N. J. A. Sloane, Apr 1977

G. Kreweras, Traitement simultané du "Problème de Young" et du "Problème de Simon Newcomb", Cahiers du Bureau Universitaire de Recherche Opérationnelle. Institut de Statistique, Université de Paris, 10 (1967), 23-31.

G. Kreweras, Traitement simultané du "Problème de Young" et du "Problème de Simon Newcomb", Cahiers du Bureau Universitaire de Recherche Opérationnelle. Institut de Statistique, Université de Paris, 10 (1967), 23-31. [Annotated scanned copy]

R. Munafo, C(n,3)C(n-1,3)/4 [From Robert Munafo, Jun 18 2009]

Simon Plouffe, Approximations de séries génératrices et quelques conjectures, Dissertation, Université du Québec à Montréal, 1992.

Simon Plouffe, 1031 Generating Functions and Conjectures, Université du Québec à Montréal, 1992.

Index entries for linear recurrences with constant coefficients, signature (7,-21,35,-35,21,-7,1).

FORMULA

a(n) = C(n, 3)C(n-1, 3)/4 = A000292(n-3)*A000292(n-2)/4 = n((n-1)(n-2))^2(n-3)/144.

E.g.f.: 1/144*x^4*(6 + 6*x + x^2)*exp(x). - Vladeta Jovovic, Jan 29 2003

a(n) = sum(sum(sum(sum(1 + sum(5*n))))) = sum (A006414). - Xavier Acloque, Oct 08 2003

a(n) = C(n, 6) + 3*C(n+1, 6) + C(n+2, 6). - Mike Zabrocki, Aug 26 2004

G.f.: z^4*(1 + 3z + z^2)/(1-z)^7. - Emeric Deutsch, Jun 20 2005

a(n) = C(n-2, n-4)*C(n-1, n-3)*C(n, n-2)/18. - Zerinvary Lajos, Jul 29 2005

a(n) = C(n,4)C(n,3)/n. - Mitch Harris, Jul 06 2006

a(n+2) = 1/4*sum {1 <= x_1, x_2 <= n} x_1*x_2*(det V(x_1,x_2))^2 = 1/4*sum {1 <= i,j <= n} i*j*(i-j)^2, where V(x_1,x_2} is the Vandermonde matrix of order 2. - Peter Bala, Sep 21 2007

a(n) = C(n-1,3)^2 - C(n-1,2)*C(n-1,4). - Gary Detlefs, Dec 05 2011

a(n) = A000292(A000217(n-1)) - A000217(A000292(n-1)). - Ivan N. Ianakiev, Jun 17 2014

a(n) = Product_{i=1..3} A002378(n-4+i)/A002378(i). - Bruno Berselli, Nov 12 2014 (Rewritten, Set 01 2016.)

Sum_{n>=4} 1/a(n) = 238 - 24*Pi^2. - Jaume Oliver Lafont, Jul 10 2017

MAPLE

A006542:=-(1+3*z+z**2)/(z-1)**7; # conjectured by Simon Plouffe in his 1992 dissertation

A006542:=n->n*((n-1)*(n-2))^2*(n-3)/144; seq(A006542(n), n=4..40); # Wesley Ivan Hurt, Jun 17 2014

MATHEMATICA

Table[Binomial[n, 3] * Binomial[n-1, 3]/4, {n, 4, 40}]

PROG

(PARI) a(n)=n*((n-1)*(n-2))^2*(n-3)/144

(MAGMA) [ n*((n-1)*(n-2))^2*(n-3)/144 : n in [4..40] ]; // Wesley Ivan Hurt, Jun 17 2014

CROSSREFS

The expression binomial(m+n-1,n)^2-binomial(m+n,n+1)*binomial(m+n-2,n-1) for the values m = 2 through 14 produces the sequences A000012, A000217, A002415, A006542, A006857, A108679, A134288, A134289, A134290, A134291, A140925, A140935, A169937.

Cf. A001263, A002378, A004068, A005585, A005891, A006322, A006414, A047819, A107891, A114242.

Fourth column of the table of Narayana numbers A001263.

Apart from a scale factor, a column of A124428.

Sequence in context: A008531 A051230 A008413 * A237655 A261648 A086462

Adjacent sequences:  A006539 A006540 A006541 * A006543 A006544 A006545

KEYWORD

nonn,easy,changed

AUTHOR

N. J. A. Sloane

EXTENSIONS

Zabroki and Lajos formulas offset corrected by Gary Detlefs, Dec 05 2011

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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified August 17 06:02 EDT 2017. Contains 290635 sequences.