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A007457 Number of (j,k): j+k=n, (j,n)=(k,n)=1, j,k squarefree.
(Formerly M0224)
2
0, 1, 2, 2, 2, 2, 4, 4, 2, 2, 4, 4, 6, 4, 4, 6, 8, 6, 6, 6, 4, 8, 8, 8, 8, 8, 8, 6, 10, 8, 10, 10, 8, 12, 8, 10, 14, 12, 10, 12, 16, 10, 18, 14, 12, 14, 16, 14, 16, 14, 10, 16, 20, 14, 12, 16, 14, 20, 18, 14, 22, 20, 16, 20 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Terms are even or 1: range = A004275. [Reinhard Zumkeller, Sep 26 2011]

REFERENCES

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Ernesto Bruno Cossi, Joachim Herzog, Paul R. Smith and Richard Stong, Problem 6623, Amer. Math. Monthly, 99 (1992), 573-575.

R. G. Wilson, V, Letter to N. J. A. Sloane, Oct. 1993

MATHEMATICA

a[n_] := Count[ Table[ If[ SquareFreeQ[j] && GCD[j, n] == 1, If[k = n-j; SquareFreeQ[k] && GCD[k, n] == 1, 1]], {j, 1, n-1}], 1]; Table[a[n], {n, 1, 64}](* Jean-Fran├žois Alcover, Nov 28 2011 *)

PROG

(Haskell)

a007457 n = length [k | k <- [1..n-1], gcd k n == 1, a008966 k == 1,

                        let j = n - k, gcd j n == 1, a008966 j == 1]

-- Reinhard Zumkeller, Sep 26 2011

CROSSREFS

Cf. A073311.

Sequence in context: A151565 A060632 A160407 * A119802 A237120 A060369

Adjacent sequences:  A007454 A007455 A007456 * A007458 A007459 A007460

KEYWORD

nonn,nice,easy

AUTHOR

N. J. A. Sloane, Robert G. Wilson v

STATUS

approved

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Last modified November 15 19:54 EST 2018. Contains 317240 sequences. (Running on oeis4.)