

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), 573575.
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 = nj; SquareFreeQ[k] && GCD[k, n] == 1, 1]], {j, 1, n1}], 1]; Table[a[n], {n, 1, 64}](* JeanFrançois Alcover, Nov 28 2011 *)


PROG

(Haskell)
a007457 n = length [k  k < [1..n1], 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



