login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A004125 Sum of remainders of n mod k, for k = 1, 2, 3, ..., n.
(Formerly M3213)
68
0, 0, 1, 1, 4, 3, 8, 8, 12, 13, 22, 17, 28, 31, 36, 36, 51, 47, 64, 61, 70, 77, 98, 85, 103, 112, 125, 124, 151, 138, 167, 167, 184, 197, 218, 198, 233, 248, 269, 258, 297, 284, 325, 328, 339, 358, 403, 374, 414, 420, 449, 454, 505, 492, 529, 520, 553, 578, 635, 586, 645, 672 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

COMMENTS

Row sums of A051778, A048158. Antidiagonal sums of A051127. - L. Edson Jeffery, Mar 03 2012

Let u_m(n) = Sum_{k=1..n} (n^m mod k^m) with m integer. As n-->+oo, u_m(n) ~ (n^(m+1))*(1-(1/(m+1))*Zeta(1+1/m)). Proof: using Riemann sums, we have u_m(n) ~ (n^(m+1))*int(((1/x)[nonascii character here])*(1-floor(x^m)/(x^m)),x=1..+oo) and the result follows. - Yalcin Aktar, Jul 30 2008 [x is the real variable of integration. The nonascii character (which was illegible in the original message) is probably some form of multiplication sign. I suggest that we leave it the way it is for now. - N. J. A. Sloane, Dec 07 2014]

Also the alternating row sums of A236112. - Omar E. Pol, Jan 26 2014

If n is prime then a(n) = a(n-1) + n - 2. - Omar E. Pol, Mar 19 2014

If n is a power of 2 greater than 1 then a(n) = a(n-1). - David Morales Marciel, Oct 21 2015

It appears that if n is a even perfect number then a(n) = a(n-1) - 1. - Omar E. Pol, Oct 21 2015

Partial sums of A235796. - Omar E. Pol, Jun 26 2016

REFERENCES

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

T. D. Noe, Table of n, a(n) for n = 1..1000

Jeffrey Shallit, Problem E2817, Amer. Math. Monthly, vol. 87, p 137, 1980.

FORMULA

a(n) = n^2 - Sum_{k=1..n} sigma(k) = A000290(n) - A024916(n), hence asymptotically a(n) = n^2*(1-Pi^2/12) + O(n*log(n)^(2/3)). - Benoit Cloitre, Apr 28 2002. Asymptotics corrected/improved by Charles R Greathouse IV, Feb 22 2015

a(n) = A008805(n-3) + A049798(n-1), for n>2. - Carl Najafi, Jan 31 2013

a(n) = A000217(n-1) - A153485(n). - Omar E. Pol, Jan 28 2014

G.f.: x^2/(1-x)^3 - (1-x)^(-1) * Sum_{k>=1} k*x^(2*k)/(1-x^k). - Robert Israel, Aug 13 2015

EXAMPLE

a(5) = 4. The remainder when 5 is divided by 2,3,4 respectively is 1,2,1 and their sum = 4.

MAPLE

A004125 := n -> add( modp(n, k), k=2..n); /* much faster and unambiguous; "a mod b" may be mods(a, b) */ # M. F. Hasler, Nov 22 2007

MATHEMATICA

Table[Sum[Mod[n, k], {k, 2, n-1}], {n, 70}] (* Harvey P. Dale, Nov 23 2011 *)

Accumulate[Table[2n-1-DivisorSigma[1, n], {n, 70}]] (* Harvey P. Dale, Jul 11 2014 *)

PROG

(PARI) A004125(n)=sum(k=2, n, n%k) \\ M. F. Hasler, Nov 22 2007

(Visual Basic in Excel)

Sub SumMod()

  X = 1

  Do While X <= 200

    Y = 2

    Z = 0

    Cells(X, 1).Value = X

    Do While Y <= X

      Z = Z + (X Mod Y)

      Y = Y + 1

    Loop

    Cells(X, 2).Value = Z

    X = X + 1

  Loop

End Sub ' Kevin Irwin (kevin.irwin(AT)aya.yale.edu), Feb 14 2010

(Haskell)

a004125 n = sum $ map (mod n) [1..n]

-- Reinhard Zumkeller, Jan 28 2011.

(MAGMA) [&+[n mod r: r in [1..n]]: n in [1..70]]; // Bruno Berselli, Jul 06 2014

CROSSREFS

Cf. A000290, A006218, A023196, A048158, A050482, A051778, A120444 (first differences).

Sequence in context: A134390 A021699 A131416 * A137924 A171527 A240969

Adjacent sequences:  A004122 A004123 A004124 * A004126 A004127 A004128

KEYWORD

nonn,easy,nice

AUTHOR

N. J. A. Sloane, Jeffrey Shallit

EXTENSIONS

Edited by M. F. Hasler, Apr 18 2015

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified March 24 06:12 EDT 2017. Contains 283984 sequences.