|
| |
|
|
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; internal format)
|
|
|
|
OFFSET
| 1,3
|
|
|
COMMENTS
| Terms are even or 1: range = A004275. [Reinhard Zumkeller, Sep 26 2011]
|
|
|
REFERENCES
| Problem 6623, Amer. Math. Monthly, 99 (1992), 573-575.
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
|
|
|
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}](* From 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 A060369 A179004
Adjacent sequences: A007454 A007455 A007456 * A007458 A007459 A007460
|
|
|
KEYWORD
| nonn,nice,easy
|
|
|
AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Robert G. Wilson v (rgwv(AT)rgwv.com)
|
| |
|
|
