



1, 5, 23, 53, 95, 149, 215, 293, 383, 485, 599, 725, 863, 1013, 1175, 1349, 1535, 1733, 1943, 2165, 2399, 2645, 2903, 3173, 3455, 3749, 4055, 4373, 4703, 5045, 5399, 5765, 6143, 6533, 6935, 7349, 7775, 8213, 8663, 9125, 9599, 10085, 10583, 11093, 11615
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OFFSET

0,2


COMMENTS

Also: The numerators in the j=2 column of the array a(i,j) defined in A140825, where the columns j=0 and j=1 are represented by A000012 and A005408. This could be extended to column j=3: 1, 1, 9, 55, 161... The common feature of these sequences derived from a(i,j) is that their jth differences are constant sequences defined by A091137(j).
a(n) is the set of all k such that 6k+6 is a perfect square.  Gary Detlefs, Mar 04 2010
The identity (6n^21)^2(9n^23)*(2n)^2=1 can be written as a(n+1)^2A157872(n)*A005843(n+1)^2=1.  Vincenzo Librandi, Feb 05 2012
Apart from first term, sequence found by reading the line from 5, in the direction 5, 23,..., in the square spiral whose vertices are the generalized pentagonal numbers A001318.  Omar E. Pol, Jul 18 2012


REFERENCES

P. Curtz, Integration .. Centre de Calcul Scientifique de l' Armement,Arcueil, (1969) 2836.


LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (3,3,1).


FORMULA

a(n) = 2*a(n1)  a(n2) + 12.
First differences: a(n+1)  a(n) = A017593(n).
Second differences: A071593(n+1)  A071593(n)=12.
G.f.: (18*x5*x^2)/(x1)^3.  Jaume Oliver Lafont, Aug 30 2009
a(n) = a(n1) +12n 6.  Vincenzo Librandi, Feb 05 2012
a(n) = 3*a(n1) 3*a(n2) +a(n3).  Vincenzo Librandi, Feb 05 2012
a(n) = A033581(n)  1.  Omar E. Pol, Jul 18 2012
a(n) = A032528(2n)  1.  Adriano Caroli, Jul 21 2013
For n>0, a(n) = floor(3/(cosh(1/n)  1)) = floor(1/(n*sinh(1/n)  1)); for similar formulas for cosine and sine, see A033581.  Clark Kimberling, Oct 19 2014, corrected by M. F. Hasler, Oct 21 2014


MATHEMATICA

LinearRecurrence[{3, 3, 1}, {1, 5, 23}, 40] (* Vincenzo Librandi, Feb 05 2012 *)


PROG

(PARI) a(n)=6*n^21 \\ Charles R Greathouse IV, Jun 01 2011
(MAGMA) [6*n^2  1: n in [0..50]]; // Vincenzo Librandi, Jun 02 2011


CROSSREFS

Cf. A005843, A157872.
Sequence in context: A127200 A147113 A135771 * A247657 A241099 A090686
Adjacent sequences: A140808 A140809 A140810 * A140812 A140813 A140814


KEYWORD

sign,easy


AUTHOR

Paul Curtz, Jul 16 2008


EXTENSIONS

Edited and extended by R. J. Mathar, Aug 06 2008
Better description Ray Chandler, Feb 03 2009


STATUS

approved



