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A081436 Diagonal in array of n-gonal numbers A081422. 23
1, 7, 24, 58, 115, 201, 322, 484, 693, 955, 1276, 1662, 2119, 2653, 3270, 3976, 4777, 5679, 6688, 7810, 9051, 10417, 11914, 13548, 15325, 17251, 19332, 21574, 23983, 26565, 29326, 32272, 35409, 38743, 42280, 46026, 49987, 54169, 58578, 63220 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

One of a family of sequences with palindromic generators.

Also as A(n) = (1/6)*(6*n^3 - 3*n^2 + 3*n), n>0: structured pentagonal diamond numbers (vertex structure 5). (Cf. A004068 = alternate vertex; A000447 = structured diamonds; A100145 for more on structured numbers.) - James A. Record (james.record(AT)gmail.com), Nov 07 2004

Sequence of the absolute values of the z^1 coefficients of the polynomials in the GF4 denominators of A156933. See A157705 for background information. - Johannes W. Meijer, Mar 07 2009

Row 1 of the convolution arrays A213831 and A213833. - Clark Kimberling, Jul 04 2012

Partial sums of A056109. - J. M. Bergot, Jun 22 2013

Number of ordered pairs of intersecting multisets of size 2, each chosen with repetition from {1,...,n}. - Robin Whitty, Feb 12 2014

Row sums of A244418. - L. Edson Jeffery, Jan 10 2015

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..5000

J. A. Dias da Silva and P. J. Freitas, Counting Spectral Radii of Matrices with Positive Entries, arXiv preprint arXiv:1305.1139, 2013

Theorem of the Day, Lovász Local Lemma example involving intersecting pairs of multisets

Index entries for linear recurrences with constant coefficients, signature (4,-6,4,-1)

FORMULA

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

G.f.: (1+x)*(1+2*x)/(1-x)^4. (Convolution of A005408 and A016777.)

a(n) = A110449(n, n-1), for n>1.

a(n) = (n+1)*T(n+1) + n*T(n), where T( ) are triangular numbers. Binomial transform of [1, 6, 11, 6, 0, 0, 0,...]. - Gary W. Adamson, Dec 28 2007

MAPLE

A081436 := proc(n)

    (n+1)*(2*n^2+3*n+2)/2 ;

end proc:

seq(A081436(n), n=0..60) ; # R. J. Mathar, Jun 26 2013

PROG

(MAGMA) [(2*n^3+5*n^2+5*n+2)/2: n in [0..40]]; // Vincenzo Librandi, Jul 19 2011

(PARI) a(n)=n^3+5/2*n*(n+1)+1 \\ Charles R Greathouse IV, Jun 20 2013

CROSSREFS

Cf. A081434, A081435, A081437, A156933, A157705, A244418.

Sequence in context: A079671 A212511 A100454 * A024205 A008779 A062449

Adjacent sequences:  A081433 A081434 A081435 * A081437 A081438 A081439

KEYWORD

easy,nonn

AUTHOR

Paul Barry, Mar 21 2003

EXTENSIONS

G.f. simplified and crossrefs added by Johannes W. Meijer, Mar 07 2009

STATUS

approved

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Last modified June 29 01:22 EDT 2017. Contains 288855 sequences.