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A083531
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First difference sequence of A002191. Differences between possible values for sum of divisors of n.
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7
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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
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history;
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internal format)
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OFFSET
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1,1
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LINKS
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Michael De Vlieger, Table of n, a(n) for n = 1..10000
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EXAMPLE
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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)
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MATHEMATICA
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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 *)
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CROSSREFS
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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
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KEYWORD
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nonn
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AUTHOR
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Labos Elemer, May 20 2003
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STATUS
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approved
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