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!)
A085584 Number of (3412,2341)-, (3412,4123)- and (3412,52341)-avoiding involutions in S_n. 0
1, 2, 4, 9, 20, 45, 100, 222, 491, 1086, 2401, 5310, 11744, 25977, 57460, 127101, 281144, 621882, 1375579, 3042726, 6730385, 14887338, 32930188, 72840249, 161119700, 356390301, 788321020, 1743734406, 3857070395, 8531684622 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..30.

E. S. Egge, Restricted 3412-Avoiding Involutions: Continued Fractions, Chebyshev Polynomials and Enumerations, sec. 8

FORMULA

G.f. (1-x^2)*(1-x)^2/(1-3*x+x^2+3*x^3-3*x^4).

MATHEMATICA

CoefficientList[Series[(1-x^2)(1-x)^2/(1-3x+x^2+3x^3-3x^4), {x, 0, 40}], x] (* Harvey P. Dale, May 28 2017 *)

CROSSREFS

Sequence in context: A091620 A208738 A108469 * A080019 A052534 A213411

Adjacent sequences:  A085581 A085582 A085583 * A085585 A085586 A085587

KEYWORD

nonn,easy

AUTHOR

Ralf Stephan, Jul 06 2003

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 February 24 00:51 EST 2020. Contains 332195 sequences. (Running on oeis4.)