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A074882 Number of integers in {1, 2, ..., sigma(n)} that are coprime to n. 0
1, 2, 3, 4, 5, 4, 7, 8, 9, 7, 11, 9, 13, 10, 13, 16, 17, 13, 19, 17, 19, 16, 23, 20, 25, 19, 27, 24, 29, 19, 31, 32, 29, 25, 34, 31, 37, 28, 35, 36, 41, 27, 43, 38, 42, 34, 47, 41, 49, 38, 45, 45, 53, 40, 53, 51, 51, 43, 59, 45, 61, 46, 60, 64, 63, 43, 67, 59, 61, 50, 71, 65, 73 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Compare the definition of a(n) to phi(n) = number of integers in {1, 2, ..., n} that are coprime to n.

LINKS

Table of n, a(n) for n=1..73.

EXAMPLE

There are four numbers in {1, 2, ..., sigma(4) = 7} that are coprime to 4, i.e. 1, 3, 5, 7. Hence a(4) = 4.

MATHEMATICA

h[n_] := Module[{l}, l = {}; For[i = 1, i <= DivisorSigma[1, n], i++, If[GCD[i, n] == 1, l = Append[l, i]]]; l]; Table[Length[h[i]], {i, 1, 100}]

CROSSREFS

Sequence in context: A130065 A079881 A058084 * A273284 A079867 A273290

Adjacent sequences:  A074879 A074880 A074881 * A074883 A074884 A074885

KEYWORD

nonn

AUTHOR

Joseph L. Pe, Oct 04 2002

STATUS

approved

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Last modified June 5 15:37 EDT 2020. Contains 334852 sequences. (Running on oeis4.)