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A074919 Number of integers in {1, 2, ..., phi(n)} that are coprime to n. 4
1, 1, 2, 1, 4, 1, 6, 2, 4, 2, 10, 1, 12, 3, 5, 4, 16, 2, 18, 3, 7, 5, 22, 3, 16, 6, 12, 5, 28, 2, 30, 8, 13, 8, 17, 4, 36, 9, 15, 6, 40, 3, 42, 9, 13, 11, 46, 5, 36, 8, 21, 11, 52, 6, 29, 10, 23, 14, 58, 4, 60, 15, 20, 16, 36, 6, 66, 15, 29, 8, 70, 8, 72, 18, 21, 17, 47, 7, 78, 13, 36 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

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..81.

EXAMPLE

There are four numbers in {1, 2, ..., phi(8) = 4} that are coprime to 8, i.e. 1, 3. Hence a(8) = 2.

MAPLE

A074919 := proc(n)

    local a, k ;

    a := 0 ;

    for k from 1 to numtheory[phi](n) do

        if igcd(k, n) = 1 then

            a := a+1 ;

        end if;

    end do:

    a ;

end proc:

seq(A074919(n), n=1..30) ; # R. J. Mathar, Feb 21 2017

MATHEMATICA

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

PROG

(PARI) a(n)=sum(k=1, eulerphi(n), 1==gcd(k, n)); \\ Joerg Arndt, Feb 21 2017

CROSSREFS

Cf. A000010.

Sequence in context: A074643 A060794 A300716 * A138009 A131755 A305812

Adjacent sequences:  A074916 A074917 A074918 * A074920 A074921 A074922

KEYWORD

nonn

AUTHOR

Joseph L. Pe, Oct 04 2002

STATUS

approved

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Last modified June 15 16:13 EDT 2019. Contains 324142 sequences. (Running on oeis4.)