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A083531 First difference sequence of A002191. Differences between possible values for sum of divisors of n. 5
2, 1, 2, 1, 1, 4, 1, 1, 1, 3, 2, 4, 4, 2, 1, 1, 4, 2, 1, 1, 2, 2, 4, 6, 2, 1, 3, 2, 1, 5, 4, 2, 4, 2, 4, 6, 1, 2, 3, 2, 4, 2, 4, 2, 2, 2, 6, 1, 3, 2, 1, 1, 4, 1, 5, 2, 4, 6, 2, 4, 2, 2, 2, 2, 4, 3, 3, 2, 4, 2, 1, 3, 6, 2, 1, 3, 2, 4, 6, 2, 4, 1, 5, 2, 4, 2, 4, 6, 2, 6, 4, 3, 1, 2, 2, 4, 2, 4, 2, 6, 2, 2, 2, 4, 6 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Michael De Vlieger, Table of n, a(n) for n = 1..10000

EXAMPLE

8 and 12 are the 6th and 7th possible values for sigma(x), since they are sum of divisors of x = 7 and x = 11 respectively, while 9, 10, 11 are impossible ones so 12 - 8 = 4 = a(6) = A002191(7) - A002191(6).

From Michael De Vlieger, Jul 22 2017: (Start)

First position of values:

Value   First position

    1         2

    2         1

    3        10

    4         6

    5        30

    6        24

    7       277

    8       165

    9       509

   10       150

   11       824

   12       400

   13     10970

   14      1400

   15     10448

   16      1182

   17     18731

   18      2218

   19    209237

   20      3420

   21    127385

   22      6910

   23     28899

   24      5377

(End)

MATHEMATICA

t=Table[DivisorSigma[1, w], {w, 1, 25000}]; u=Union[%]; Delete[u-RotateRight[u], 1]

(* Second program: *)

With[{nn = 300}, Differences@ TakeWhile[Union@ DivisorSigma[1, Range@ nn], # < nn &]] (* Michael De Vlieger, Jul 22 2017 *)

CROSSREFS

Cf. A002191, A007609, A007369, A083532, A083533, A083534, A083535, A083536.

Sequence in context: A134303 A078997 A024680 * A003417 A158986 A079900

Adjacent sequences:  A083528 A083529 A083530 * A083532 A083533 A083534

KEYWORD

nonn

AUTHOR

Labos Elemer, May 20 2003

STATUS

approved

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Last modified September 25 02:13 EDT 2017. Contains 292441 sequences.