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A074818 Number of integers in {1, 2, ..., prime(n)} that are coprime to n. 0
2, 2, 4, 4, 9, 5, 15, 10, 16, 12, 29, 13, 38, 19, 26, 27, 56, 21, 64, 29, 42, 36, 80, 30, 78, 47, 69, 46, 106, 31, 123, 66, 84, 66, 103, 51, 153, 78, 104, 70, 175, 52, 187, 88, 106, 96, 207, 75, 195, 92, 147, 111, 237, 84, 187, 113, 170, 131, 273, 75, 279, 142, 176 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

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..63.

EXAMPLE

There are five numbers in {1, 2, ..., prime(6) = 13} that are coprime to 6, i.e. 1, 5, 7, 11, 13. Hence a(6) = 5.

MATHEMATICA

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

CROSSREFS

Sequence in context: A287489 A288045 A292941 * A322112 A324409 A110199

Adjacent sequences:  A074815 A074816 A074817 * A074819 A074820 A074821

KEYWORD

nonn

AUTHOR

Joseph L. Pe, Oct 04 2002

STATUS

approved

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Last modified October 30 03:24 EDT 2020. Contains 338076 sequences. (Running on oeis4.)