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A027480 a(n) = n*(n+1)*(n+2)/2. 41
0, 3, 12, 30, 60, 105, 168, 252, 360, 495, 660, 858, 1092, 1365, 1680, 2040, 2448, 2907, 3420, 3990, 4620, 5313, 6072, 6900, 7800, 8775, 9828, 10962, 12180, 13485, 14880, 16368, 17952, 19635, 21420, 23310, 25308, 27417, 29640, 31980, 34440 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Write the integers in groups: 0; 1,2; 3,4,5; 6,7,8,9; ... and add the groups: a(n) = Sum_{j=0..n} (A000217(n)+j), row sums of the triangular view of A001477. - Asher Auel (asher.auel(AT)reed.edu), Jan 06 2000

With offset = 2, a(n) is the number of edges of the line graph of the complete graph of order n, L(K_n). - Roberto E. Martinez II, Jan 07 2002

Also the total number of pips on a set of dominoes of type n. (A "3" domino set would have 0-0, 0-1, 0-2, 0-3, 1-1, 1-2, 1-3, 2-2, 2-3, 3-3.) - Gerard Schildberger, Jun 26 2003. See A129533 for generalization to n-armed "dominoes". - N. J. A. Sloane, Jan 06 2016

Common sum in an (n+1) X (n+1) magic square with entries (0..n^2-1).

Alternate terms of A057587. - Jeremy Gardiner, Apr 10 2005

If Y is a 3-subset of an n-set X then, for n>=5, a(n-5) is the number of 4-subsets of X which have exactly one element in common with Y. Also, if Y is a 3-subset of an n-set X then, for n>=5, a(n-5) is the number of (n-5)-subsets of X which have exactly one element in common with Y. - Milan Janjic, Dec 28 2007

These numbers, starting with 3, are the denominators of the power series f(x)=(1-x)^2 * log(1/(1-x)), if the numerators are kept at 1. This sequence of denominators starts at the term x^3/3. - Miklos Bona (bona(AT)math.ufl.edu), Feb 18 2009

a(n) is the number of triples (w,x,y) having all terms in {0,,,.n} and satisfying at least one of the inequalities x+y<w, y+w<x, w+x<y. - Clark Kimberling, Jun 14 2012

Comments from Martin Licht, Dec 04 2016 (Start)

Let b(n) = (n+1)(n+2)(n+3)/2 (the same sequence, but with a different offset). Then (see Arnold et al., 2006):

b(n) is the dimension of the Nédélec space of the second kind of polynomials of order n over a tetrahedron.

b(n-1) is the dimension of the curl-conforming Nédélec space of the first kind of polynomials of order n with tangential boundary conditions over a tetrahedron.

b(n) is the dimension of the divergence-conforming Nédélec space of the first kind of polynomials of order n with normal boundary conditions over a tetrahedron. (End)

After a(0), the digital root has period 9: repeat [3, 3, 3, 6, 6, 6, 9, 9, 9]. - Peter M. Chema, Jan 19 2017

LINKS

T. D. Noe, Table of n, a(n) for n = 0..1000

D. N. Arnold, R. S. Falk, R. Winther, Finite element exterior calculus, homological techniques, and applications, Acta numerica 15 (2006), 1-155.

S. Gartenhaus, Odd Order Pandiagonal Latin and Magic Cubes in Three and Four Dimensions, arXiv:math/0210275 [math.CO], 2002.

Index entries for sequences related to dominoes

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

FORMULA

a(n) = a(n-1) + A050534(n) = 3*A000292(n-1) = A050534(n)-A050534(n-1).

a(n) = n*binomial(2+n, 2). - Zerinvary Lajos, Jan 10 2006

a(n) = numbperm(n,3)/2, n>=2 [where numbperm(n, k) = n!/(n-k)!]. - Zerinvary Lajos, Apr 26 2007

a(n) = A007531(n+2)/2. - Zerinvary Lajos, Jul 17 2006

Starting with offset 1 = binomial transform of [3, 9, 9, 3, 0, 0, 0]. - Gary W. Adamson, Oct 25 2007

G.f.: 3*x/(x-1)^4. a(n)=4*a(n-1)-6*a(n-2)+4*a(n-3)-a(n-4). - R. J. Mathar, Apr 07 2009

a(n) = Sum_{i=0..n} n*(n - i) + 2*i. [Bruno Berselli, Jan 13 2016]

From Ilya Gutkovskiy, Aug 07 2016: (Start)

E.g.f.: x*(6 + 6*x + x^2)*exp(x)/2.

a(n) = Sum_{k=0..n} A045943(k).

Sum_{n>=1} 1/a(n) = 1/2.

Sum_{n>=1) (-1)^(n+1)/a(n) = (8*log(2) - 5)/2 = 0.2725887222397812... (End)

EXAMPLE

Row sums of n consecutive integers, starting at 0, seen as a triangle:

.

0   | 0

3   | 1  2

12  | 3  4  5

30  | 6  7  8 9

60  | 10 11 12 13 14

105 | 15 16 17 18 19 20

MAPLE

[seq(3*binomial(n, 3), n=2..37)]; # Zerinvary Lajos, Nov 24 2006

a:=n->sum ((j+n)*(n+2)/3, j=0..n): seq(a(n), n=0..35); # Zerinvary Lajos, Dec 17 2006

MATHEMATICA

Table[(m^3 - m)/2, {m, 36}] (* Zerinvary Lajos, Mar 21 2007 *)

LinearRecurrence[{4, -6, 4, -1}, {0, 3, 12, 30}, 40] (* Harvey P. Dale, Oct 10 2012 *)

CoefficientList[Series[3 x / (x - 1)^4, {x, 0, 40}], x] (* Vincenzo Librandi, Nov 14 2014 *)

PROG

(PARI) a(n)=3*binomial(n+2, 3) \\ Charles R Greathouse IV, May 23, 2011

(MAGMA) [n*(n+1)*(n+2)/2: n in [0..40]]; // Vincenzo Librandi, Nov 14 2014

CROSSREFS

1/beta(n, 3) in A061928.

Cf. A057587, A006003, A254407.

A row of array in A129533.

Cf. similar sequences of the type n*(n+1)*(n+k)/2 listed in A267370.

Cf. A281258.

Sequence in context: A164013 A057671 * A135503 A048088 A064181 A089143

Adjacent sequences:  A027477 A027478 A027479 * A027481 A027482 A027483

KEYWORD

nonn,nice,easy

AUTHOR

Olivier Gérard and Ken Knowlton (kcknowlton(AT)aol.com)

STATUS

approved

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Last modified June 28 13:23 EDT 2017. Contains 288835 sequences.