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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A081254 Numbers k such that A081252(m)/m^2 has a local maximum for m = k. 15
1, 3, 6, 13, 26, 53, 106, 213, 426, 853, 1706, 3413, 6826, 13653, 27306, 54613, 109226, 218453, 436906, 873813, 1747626, 3495253, 6990506, 13981013, 27962026, 55924053, 111848106, 223696213, 447392426, 894784853, 1789569706, 3579139413 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

The limit of the local maxima, lim_{m->inf} A081252(m)/m^2 = 1/10. For local minima cf. A081253.

Row sums of the triangle A181971. - Reinhard Zumkeller, Jul 09 2012

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Klaus Brockhaus, Illustration for A053646, A081252, A081253 and A081254

FORMULA

a(n) = floor(2^(n-1)*5/3). [corrected by Michel Marcus, Sep 21 2018]

a(n) = a(n-2) + 5*2^(n-3) for n > 2;

a(n+2) - a(n) = A020714(n-1);

a(n) + a(n-1) = A052549(n-1) for n > 1;

a(2*n+1) = A020989(n); a(2n) = A072197(n-1);

a(n+1) - a(n) = A048573(n-1).

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

a(n) = 5*2^(n-1)/3 + (-1)^n/6-1/2. a(n) = 2*a(n-1) + (1+(-1)^n)/2, a(1)=1. - Paul Barry, Mar 24 2003

a(2n) = 2*a(2*n-1) + 1, a(2*n+1) = 2*a(2*n), a(1)=1. a(n) = A000975(n-1) + 2^(n-1). - Philippe Deléham, Oct 15 2006

a(n) = A005578(n) + A000225(n-1).  - Yuchun Ji, Sep 21 2018

EXAMPLE

13 is a term since A081252(12)/12^2 = 15/144 = 0.104, A081252(13)/13^2 = 18/169 = 0.107, A081252(14)/14^2 = 20/196 = 0.102.

MAPLE

seq(floor(2^(n-1)*5/3), n=1..35); # Muniru A Asiru, Sep 20 2018

MATHEMATICA

CoefficientList[Series[-(x^2-x-1)*x/((x-1)*(x+1)*(2*x-1)), {x, 1, 33}], x] (* Vincenzo Librandi, Apr 04 2012 *)

a[n_]:=Floor[2^(n-1)*5/3]; Array[a, 33, 1] (* Stefano Spezia, Sep 01 2018 *)

PROG

(MAGMA) [Floor(2^(n-1)*5/3): n in [1..40]]; // Vincenzo Librandi, Apr 04 2012

(PARI) a(n) = 2^(n-1)*5\3; \\ Altug Alkan, Sep 21 2018

CROSSREFS

Cf. A000975, A020714, A020989, A048573, A052549, A053646, A072197, A081252, A081253.

Sequence in context: A265385 A019300 A072762 * A125049 A267581 A320733

Adjacent sequences:  A081251 A081252 A081253 * A081255 A081256 A081257

KEYWORD

nonn

AUTHOR

Klaus Brockhaus, Mar 17 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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified November 22 05:30 EST 2018. Contains 317453 sequences. (Running on oeis4.)