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A080856 8*n^2 - 4*n + 1. 23
1, 5, 25, 61, 113, 181, 265, 365, 481, 613, 761, 925, 1105, 1301, 1513, 1741, 1985, 2245, 2521, 2813, 3121, 3445, 3785, 4141, 4513, 4901, 5305, 5725, 6161, 6613, 7081, 7565, 8065, 8581, 9113, 9661, 10225, 10805, 11401, 12013, 12641, 13285, 13945, 14621 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

The old definition of this sequence was "Generalized polygonal numbers".

Row T(4,n) of A080853.

{a(k): 0 <= k < 3} = divisors of 25. - Reinhard Zumkeller, Jun 17 2009

Let A be the Hessenberg matrix of order n, defined by: A[1,j]=1, A[i,i]:=4, (i>1), A[i,i-1]=-1, and A[i,j]=0 otherwise. Then, for n>=3, a(n-1)= coeff(charpoly(A,x),x^(n-2)). - Milan Janjic, Jan 27 2010

Also sequence found by reading the segment (1, 5) together with the line from 5, in the direction 5, 25,..., in the square spiral whose vertices are the generalized hexagonal numbers A000217. - Omar E. Pol, Nov 05 2012

For n > 0: A049061(a(n)) = 0, when the triangle of "signed Eulerian numbers" in A049061 is seen as flattened sequence. - Reinhard Zumkeller, Jan 31 2013

LINKS

Table of n, a(n) for n=0..43.

R. Zumkeller, Enumerations of Divisors.

Index entries for linear recurrences with constant coefficients, signature (3,-3,1).

FORMULA

G.f.: (1+2*x+13*x^2)/(1-x)^3.

a(n) = A060820(n), n>0. - R. J. Mathar, Sep 18 2008

a(n) = C(n,0) + 4*C(n,1) + 16*C(n,2). - Reinhard Zumkeller, Jun 17 2009

a(n) = 16*n+a(n-1)-12 with n>0, a(0)=1. - Vincenzo Librandi, Aug 08 2010

MATHEMATICA

LinearRecurrence[{3, -3, 1}, {1, 5, 25}, 80] (* Vladimir Joseph Stephan Orlovsky, Feb 17 2012 *)

PROG

(PARI) a(n)=8*n^2-4*n+1 \\ Charles R Greathouse IV, Sep 24 2015

CROSSREFS

Cf. A005408, A000124, A016813, A086514, A000125, A058331, A002522, A161701, A161702, A161703, A000127, A161704, A161706, A161707, A161708, A161710, A161711, A161712, A161713, A161715, A006261.

Sequence in context: A146412 A228169 A152734 * A060820 A182211 A146404

Adjacent sequences:  A080853 A080854 A080855 * A080857 A080858 A080859

KEYWORD

nonn,easy

AUTHOR

Paul Barry, Feb 23 2003

EXTENSIONS

Definition replaced with the closed form by Bruno Berselli, Jan 16 2013

STATUS

approved

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Last modified May 30 06:51 EDT 2017. Contains 287302 sequences.