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1,2

Number of 6-digit numbers in base n (with leading zeros allowed) such that the sum of the first three digits equals the sum of the last three digits.

a(n) = largest coefficient of (1+...+x^(n-1))^6. - R. H. Hardin, Jul 23 2009

Vincenzo Librandi, Table of n, a(n) for n = 1..10000

M. B. Nathanson, Growth polynomials for additive quadruples and (h, k)-tuples, arXiv preprint arXiv:1305.7172, 2013

Index entries for linear recurrences with constant coefficients, signature (6,-15,20,-15,6,-1).

The sum of the squares of the number of different 3-digit numbers that add up to k (summed over all possible k's) - cf. A071817.

a(n) = n*(11*n^4+5*n^2+4)/20. Recurrence: a(n) = 6*a(n-1)-15*a(n-2)+20*a(n-3)-15*a(n-4)+6*a(n-5)-a(n-6). G.f.: x*(1+14*x+36*x^2+14*x^3+x^4)/(1-x)^6. - Vladeta Jovovic, Jun 09 2002

For n = 2 there are 20 ordered solutions (x,y,z,u,v,w) to x+y+z = u+v+w: (0,0,0,0,0,0), (0,0,1,0,0,1), (0,0,1,0,1,0), (0,0,1,1,0,0), (0,1,0,0,0,1), (0,1,0,0,1,0), (0,1,0,1,0,0), (0,1,1,0,1,1), (0,1,1,1,0,1), (0,1,1,1,1,0), (1,0,0,0,0,1), (1,0,0,0,1,0), (1,0,0,1,0,0), (1,0,1,0,1,1), (1,0,1,1,0,1), (1,0,1,1,1,0), (1,1,0,0,1,1), (1,1,0,1,0,1), (1,1,0,1,1,0), (1,1,1,1,1,1).

a(n)=A077042(n,6).

A071816 := proc(n) n*(11*n^4+5*n^2+4)/20 ; end proc: # R. J. Mathar, Sep 04 2011

(MAGMA) [n*(11*n^4+5*n^2+4)/20: n in [1..30]]; // Vincenzo Librandi, Sep 05 2011

Cf. A008528, A071817.

First differences are in A070302.

Sequence in context: A054389 A253003 A293932 * A263960 A190067 A238021

Adjacent sequences: A071813 A071814 A071815 * A071817 A071818 A071819

nonn,base,easy

Graeme McRae, Jun 07 2002

New definition from Vladeta Jovovic, Jun 09 2002

Comment revised by Franklin T. Adams-Watters, Jul 27 2009

Edited by N. J. A. Sloane, Jul 28 2009

approved