0,2

Write the integers in groups: 0; 1,2; 3,4,5; 6,7,8,9; ... and add the groups - Asher Auel (asher.auel(AT)reed.edu) Jan 06, 2000. Note that each group begins with a triangular number.

Number of edges of the line graph of the complete graph of order n, L(K_n) - Roberto E. Martinez II (remartin(AT)fas.harvard.edu), Jan 07 2002

Also the number of the total 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 (GerardS(AT)rrt.net), Jun 26 2003

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

Alternate terms of A057587. - Jeremy Gardiner (jeremy.gardiner(AT)btinternet.com), Apr 10 2005

A027480=A007531/2 - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Jul 17 2006

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 R. Janjic (agnus(AT)blic.net), Dec 28 2007

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

S. Gartenhaus, Odd order pandiagonal latin and magic cubes....

Index entries for sequences related to dominoes

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

n*C(2+n, 2). - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Jan 10 2006

a(n)=numbperm (n,3)/2, n>=2. - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Apr 26 2007

Starting with offset 1 = binomial transform of [3, 9, 9, 3, 0, 0, 0]. - Gary W. Adamson (qntmpkt(AT)yahoo.com), Oct 25 2007

[seq(3*binomial(n, 3), n=2..37)]; - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Nov 24 2006

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

a:=n->sum(binomial(n, 2), j=0..n): seq(a(n), n=1..36); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Feb 12 2007

seq(numbperm (n, 3)/2, n=2..37); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Apr 26 2007

Table[(m^3 - m)/2, {m, 36}] - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Mar 21 2007

1/beta(n, 3) in A061928.

Antidiagonal sums of array in A001477.

Cf. A057587, A006003.

Sequence in context: A101459 A051408 A057671 this_sequence A135503 A048088 A064181

Adjacent sequences: A027477 A027478 A027479 this_sequence A027481 A027482 A027483

nonn,nice,easy

Olivier Gerard (ogerard(AT)ext.jussieu.fr) and Ken Knowlton (kcknowlton(AT)aol.com)