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 A098077 a(n) = n^2*(n+1)*(2*n+1)/3. 10
 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). From Torlach Rush, Jan 05 2020: (Start) a(n) = n * A006331(n). tr(M(n)) = A006331(n). The sum of the antidiagonal of M(n) equals tr(M(n)). M(n) = M(n)' (Symmetric). M(1,) = M(,1) = A002522(n), n > 0. M(2,) = M(,2) = A087475(n), n > 0. M(3,) = M(,3) = A189834(n), n > 0. M(4,) = M(,4) = A241751(n), n > 0. (End) 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_{j=1..n} Sum_{i=1..n} (i^2 + j^2). G.f.: 2*x*(1 + 5*x + 2*x^2)/(1-x)^5. - Colin Barker, May 04 2012 E.g.f.: (1/3)*exp(x)*x*(6 + 24*x + 15*x^2 + 2*x^3) . - Stefano Spezia, Jan 06 2020 a(n) = a(n-1) + (8*n^3 - 3*n^2 + n)/3. - Torlach Rush, Jan 07 2020 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 Cf. A002522, A006331, A087475, A189834, A241751. Sequence in context: A259110 A135188 A161007 * A279264 A063663 A071253 Adjacent sequences:  A098074 A098075 A098076 * A098078 A098079 A098080 KEYWORD nonn,easy,changed 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 January 23 01:15 EST 2020. Contains 331166 sequences. (Running on oeis4.)