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!)
A003274 Number of key permutations of length n: permutations {a_i} with |a_i-a_{i-1}|=1 or 2.
(Formerly M1583)
15
1, 2, 6, 12, 20, 34, 56, 88, 136, 208, 314, 470, 700, 1038, 1534, 2262, 3330, 4896, 7192, 10558, 15492, 22724, 33324, 48860, 71630, 105002, 153912, 225594, 330650, 484618, 710270, 1040980, 1525660, 2235994, 3277040, 4802768, 7038832 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

REFERENCES

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

LINKS

R. H. Hardin, Table of n, a(n) for n=1..251, May 06 2010

S. Avgustinovich and S. Kitaev, On uniquely k-determined permutations, Discr. Math., 308 (2008), 1500-1507.

E. S. Page, Systematic generation of ordered sequences using recurrence relations, Computer J., 14 (1971), 150-153.

E. S. Page, Systematic generation of ordered sequences using recurrence relations, The Computer Journal 14 (1971), 150-153. (Annotated scanned copy)

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.

FORMULA

For n>1, a(n) = 2*A069241(n).

G.f.: x*(-1 + x - 3*x^2 + 2*x^3 - x^5)/((- 1+ x)^2*(-1 + x + x^3)).

MAPLE

A003274:=-(1-z+3*z**2-2*z**3+z**5)/(z**3+z-1)/(z-1)**2; [Conjectured by Simon Plouffe in his 1992 dissertation.]

CROSSREFS

Sequence in context: A194110 A277365 A184432 * A259470 A121315 A078878

Adjacent sequences:  A003271 A003272 A003273 * A003275 A003276 A003277

KEYWORD

nonn

AUTHOR

N. J. A. Sloane.

EXTENSIONS

Better description and g.f. from Erich Friedman.

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 11:22 EDT 2017. Contains 290635 sequences.