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A024916
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a(n) = Sum_{k=1..n} k*floor(n/k); also Sum_{k=1..n} sigma(k) where sigma(n) = sum of divisors of n (A000203).
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119
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1, 4, 8, 15, 21, 33, 41, 56, 69, 87, 99, 127, 141, 165, 189, 220, 238, 277, 297, 339, 371, 407, 431, 491, 522, 564, 604, 660, 690, 762, 794, 857, 905, 959, 1007, 1098, 1136, 1196, 1252, 1342, 1384, 1480, 1524, 1608, 1686, 1758, 1806, 1930, 1987, 2080, 2152
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,2
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COMMENTS
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Row sums of triangle A130541. E.g., a(5) = 15 = (10 + 3 + 1 + 1), sum of row 4 terms of triangle A130541. - Gary W. Adamson, Jun 03 2007
Row sums of triangle A134867. - Gary W. Adamson, Nov 14 2007
a(10^4) = 82256014, a(10^5) = 8224740835, a(10^6) = 822468118437, a(10^7) = 82246711794796; see A072692. - M. F. Hasler, Nov 22 2007
Equals row sums of triangle A158905. - Gary W. Adamson, Mar 29 2009
n is prime if and only if a(n) - a(n-1) - 1 = n. - Omar E. Pol, Dec 31 2012
Also the alternating row sums of A236104. - Omar E. Pol, Jul 21 2014
a(n) is also the total number of parts in all partitions of the positive integers <= n into equal parts. - Omar E. Pol, Apr 30 2017
a(n) is also the total area of the terraces of the step pyramid with n levels described in A245092. - Omar E. Pol, Nov 04 2017
a(n) is also the area under the Dick path described in the n-th row of A237593. - Omar E. Pol, Sep 17 2018
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REFERENCES
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Hardy and Wright, "An introduction to the theory of numbers", Oxford University Press, fifth edition, p. 266.
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LINKS
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Daniel Mondot, Table of n, a(n) for n = 1..10000 (first 1000 terms from T. D. Noe)
P. L. Patodia (pannalal(AT)usa.net), PARI program for A072692 and A024916
Peter Polm, C# program for A024916
A. Walfisz, Weylsche Exponentialsummen in der neueren Zahlentheorie, ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik, Volume 44, Issue 12, page 607, 1964.
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FORMULA
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a(n) = n^2 - A004125(n); asymptotically a(n) = n^2*Pi^2/12 + O(n*Log(n)). - Benoit Cloitre, Apr 28 2002
G.f.: (1/(1-x))*Sum_{k>=1} x^k/(1-x^k)^2. - Benoit Cloitre, Apr 23 2003
a(n) = Sum_{m=1..n} (n - (n mod m)). - Roger L. Bagula and Gary W. Adamson, Oct 06 2006
a(n) = n^2*Pi^2/12 + O(n*log(n)^(2/3)) [Walfisz]. - Charles R Greathouse IV, Jun 19 2012
a(n) = A000217(n) + A153485(n). - Omar E. Pol, Jan 28 2014
a(n) = A000292(n) - A076664(n), n > 0. - Omar E. Pol, Feb 11 2014
a(n) = A078471(n) + A271342(n). - Omar E. Pol, Apr 08 2016
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MAPLE
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A024916 := proc(n)
add(numtheory[sigma](k), k=0..n) ;
end proc: # Zerinvary Lajos, Jan 11 2009
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MATHEMATICA
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Table[Plus @@ Flatten[Divisors[Range[n]]], {n, 50}] (* Alonso del Arte, Mar 06 2006 *)
Table[Sum[n - Mod[n, m], {m, n}], {n, 50}] (* Roger L. Bagula and Gary W. Adamson, Oct 06 2006 *)
a[n_] := Sum[DivisorSigma[1, k], {k, n}]; Table[a[n], {n, 51}] (* Jean-François Alcover, Dec 16 2011 *)
Accumulate[DivisorSigma[1, Range[60]]] (* Harvey P. Dale, Mar 13 2014 *)
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PROG
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(PARI) A024916(n)=sum(k=1, n, n\k*k) \\ M. F. Hasler, Nov 22 2007
(PARI) A024916(z) = { my(s, u, d, n, a, p); s = z*z; u = sqrtint(z); p = 2; for(d=1, u, n = z\d - z\(d+1); if(n<=1, p=d; break(), a = z%d; s -= (2*a+(n-1)*d)*n/2); ); u = z\p; for(d=2, u, s -= z%d); return(s); } \\ See the link for a nicely formatted version. - P. L. Patodia (pannalal(AT)usa.net), Jan 11 2008
(PARI) A024916(n)={my(s=0, d=1, q=n); while(d<q, s+=q*(q+1+2*d)\2; d++; q=n\d; ); return(s-d*(d-1)\2*d+q*(q+1)\2); } \\ Peter Polm, Aug 18 2014
(PARI) A024916(n)={ my(s=n^2, r=sqrtint(n), nd=n, D); for(d=1, r, (1>=D=nd-nd=n\(d+1)) && (r=d-1) && break; s -= n%d*D+(D-1)*D\2*d); s - sum(d=2, n\(r+1), n%d)} \\ Slightly optimized version of Patodia's code. - M. F. Hasler, Apr 18 2015
(C#) See Polm link.
(Haskell)
a024916 n = sum $ map (\k -> k * div n k) [1..n]
-- Reinhard Zumkeller, Apr 20 2015
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CROSSREFS
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Cf. A056550, A104471(2*n-1, n), A123229, A130541, A000217, A134867, A072692, A158905, A237593, A245092.
Sequence in context: A071422 A212538 A113902 * A212539 A102216 A001182
Adjacent sequences: A024913 A024914 A024915 * A024917 A024918 A024919
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KEYWORD
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nonn,nice
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AUTHOR
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Clark Kimberling
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STATUS
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approved
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