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A256102 Numbers m such that GCD(A001008(m), m) > 1, in increasing order. 4
20, 42, 77, 110, 156, 272, 342, 506, 812, 930, 1247, 1332, 1640, 1806, 2162, 2756, 3422, 3660, 4422, 4970, 5256, 6162, 6806, 7832, 9312, 9328, 10100, 10506, 11342, 11772, 12656, 16002, 17030, 18632, 19182, 22052, 22650, 24492, 26406, 27722, 29756, 31862, 32580, 36290, 37056, 38612, 39402 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For the corresponding values of GCD(A001008(a(n)), a(n)) see A256103(n).

A001008(a(n))/A175441(a(n)) = A256103(n), n >= 1.

This means that for all values n not in the present sequence the numerator of the harmonic sum (HS) of the first n positive integers coincides with the denominator of the harmonic mean (HM) of the first n positive integers. That is, n divides the HM(n) numerator A102928(n) for n not in the present sequence.

Of course, HS(n)*HM(n) = n, n >= 1, where HS(n) = A001008(n)/A002805(n) and HM(n) = A102928(n)/A175441(n).

LINKS

Table of n, a(n) for n=1..47.

FORMULA

a(n) is the n-th smallest element of the set M:= {m positive inter | GCD(A001008(m) ,m) > 1}, n >= 1.

EXAMPLE

n=1: GCD(A001008(20), 20) = GCD(55835135, 20) = 5 = A256103(1) > 1.

A001008(20)/A175441(20) = 55835135/11167027 = 5 = A256103(1).

  Because 19 is not in this sequence 1 = GCD(A001008(19), 19) = GCD(275295799, 19).

CROSSREFS

Cf. A256103, A001008, A002805, A102928, A175441.

Sequence in context: A041798 A132762 A075228 * A128672 A290184 A126251

Adjacent sequences:  A256099 A256100 A256101 * A256103 A256104 A256105

KEYWORD

nonn,easy

AUTHOR

Wolfdieter Lang, Apr 16 2015

STATUS

approved

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Last modified February 22 12:00 EST 2018. Contains 299452 sequences. (Running on oeis4.)