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A098077 a(n) = n^2*(n+1)*(2*n+1)/3. 9
2, 20, 84, 240, 550, 1092, 1960, 3264, 5130, 7700, 11132, 15600, 21294, 28420, 37200, 47872, 60690, 75924, 93860, 114800, 139062, 166980, 198904, 235200, 276250, 322452, 374220, 431984, 496190, 567300, 645792, 732160, 826914, 930580, 1043700 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Sum of all matrix elements M(i,j) = i^2 + j^2 (i,j = 1,...,n).

Consider the partitions of 2n into two parts (p,q) where p <= q. Then a(n) is the total volume of the family of rectangular prisms with dimensions p, p and p+q. - Wesley Ivan Hurt, Apr 15 2018

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Index entries for linear recurrences with constant coefficients, signature (5,-10,10,-5,1).

FORMULA

a(n) = Sum[Sum[(i^2+j^2), {i, 1, n}], {j, 1, n}].

G.f.: 2*x*(1+5*x+2*x^2)/(1-x)^5. - Colin Barker, May 04 2012

EXAMPLE

a(2) = (1^2+1^2) + (1^2+2^2) + (2^2+1^2) + (2^2+2^2) = 2 + 5 + 5 + 8 = 20.

MATHEMATICA

Table[ Sum[i^2 + j^2, {i, n}, {j, n}], {n, 35}]

LinearRecurrence[{5, -10, 10, -5, 1}, {2, 20, 84, 240, 550}, 40] (* Vincenzo Librandi, Apr 16 2018 *)

PROG

(PARI) a(n)=n^2*(n+1)*(2*n+1)/3 \\ Charles R Greathouse IV, Oct 07 2015

CROSSREFS

Sequence in context: A259110 A135188 A161007 * A279264 A063663 A071253

Adjacent sequences:  A098074 A098075 A098076 * A098078 A098079 A098080

KEYWORD

nonn,easy

AUTHOR

Alexander Adamchuk, Oct 24 2004

EXTENSIONS

More terms from Robert G. Wilson v, Nov 01 2004

New definition from Ralf Stephan, Dec 01 2004

STATUS

approved

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Last modified November 17 03:06 EST 2019. Contains 329216 sequences. (Running on oeis4.)