This site is supported by donations to The OEIS Foundation.

 Annual appeal: Please make a donation to keep the OEIS running! Over 6000 articles have referenced us, often saying "we discovered this result with the help of the OEIS". Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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-François 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 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.