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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A261671 If n even, a(n) = 6n+3, otherwise a(n) = n. 4
3, 1, 15, 3, 27, 5, 39, 7, 51, 9, 63, 11, 75, 13, 87, 15, 99, 17, 111, 19, 123, 21, 135, 23, 147, 25, 159, 27, 171, 29, 183, 31, 195, 33, 207, 35, 219, 37, 231, 39, 243, 41, 255, 43, 267, 45, 279, 47, 291, 49, 303, 51, 315, 53, 327, 55, 339, 57, 351, 59, 363 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

REFERENCES

Although the OEIS indexes sequences by consecutive integers, it is better to think of this sequence as defined on the odd numbers 1,3,5,7,... and given by f(4m+1)=12m+3, f(4m+3)=2m+1, that is, subtract 1 and divide by 2 if the result is odd, otherwise multiply by 3. This arises in analyzing A109732.

It is conjectured that starting with any positive odd number d and iterating f, we always eventually reach either 1, 9, or 33 (see Comments in A135730).

LINKS

Colin Barker, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (0,2,0,-1).

FORMULA

From Colin Barker, Sep 13 2015: (Start)

a(n) = (3+3*(-1)^n+7*n+5*(-1)^n*n)/2.

a(n) = 2*a(n-2) - a(n-4) for n>3.

G.f.: (x^3+9*x^2+x+3) / ((x-1)^2*(x+1)^2).

(End)

PROG

(PARI) Vec((x^3+9*x^2+x+3)/((x-1)^2*(x+1)^2) + O(x^100)) \\ Colin Barker, Sep 13 2015

CROSSREFS

Cf. A109732, A135730.

Sequence in context: A134145 A134146 A085569 * A198148 A286674 A286024

Adjacent sequences:  A261668 A261669 A261670 * A261672 A261673 A261674

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane, Sep 02 2015

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 March 23 02:42 EDT 2019. Contains 321422 sequences. (Running on oeis4.)