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A085599 Number of pairs of coprimes (n-i,n+i), 1<i<n. 1
0, 0, 1, 1, 2, 1, 3, 3, 3, 3, 5, 3, 6, 5, 4, 7, 8, 5, 9, 7, 6, 9, 11, 7, 10, 11, 9, 11, 14, 7, 15, 15, 10, 15, 12, 11, 18, 17, 12, 15, 20, 11, 21, 19, 12, 21, 23, 15, 21, 19, 16, 23, 26, 17, 20, 23, 18, 27, 29, 15, 30, 29, 18, 31, 24, 19, 33, 31, 22, 23, 35, 23, 36, 35, 20 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

LINKS

Table of n, a(n) for n=1..75.

FORMULA

For n>1, a(n) = A055034(n) - ((-1)^n + 1)/2 = A000010(2*n)/2 - ((-1)^n + 1)/2. - Max Alekseyev, Jul 21 2016

EXAMPLE

n=7: (7-2,7+2)=(5,9), (7-3,7+3)=(4,10), (7-4,7+4)=(3,11), (7-5,7+5)=(2,12), (7-6,7+6)=(1,13): only three are coprime: (5,9), (3,11) and (1,13), therefore a(7)=3.

MAPLE

A085599 := proc(n)

    local i, a;

    a := 0 ;

    for i from 2 to n-1 do

        if igcd(n-i, n+i) = 1 then

            a := a+1 ;

        end if;

    end do:

    a ;

end proc: # R. J. Mathar, Jul 09 2016

CROSSREFS

Cf. A055034, A102781.

Sequence in context: A038565 A248605 A239619 * A299966 A302395 A110425

Adjacent sequences:  A085596 A085597 A085598 * A085600 A085601 A085602

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Jul 06 2003

EXTENSIONS

Definition corrected by Ray Chandler, Jul 09 2016

STATUS

approved

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Last modified October 20 22:05 EDT 2019. Contains 328291 sequences. (Running on oeis4.)