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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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