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A100613 Number of elements in the set {(x,y): 1 <= x,y <= n, gcd(x,y) > 1}. 7
0, 1, 2, 5, 6, 13, 14, 21, 26, 37, 38, 53, 54, 69, 82, 97, 98, 121, 122, 145, 162, 185, 186, 217, 226, 253, 270, 301, 302, 345, 346, 377, 402, 437, 458, 505, 506, 545, 574, 621, 622, 681, 682, 729, 770, 817, 818, 881, 894, 953, 990, 1045, 1046, 1117, 1146, 1209 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..1000

FORMULA

a(n) = A000290(n) - A018805(n) = A185670(n) + A063985(n). - Reinhard Zumkeller, Jan 21 2013

a(n) = Sum_{k = 2..n} A242114(n,k). - Reinhard Zumkeller, May 04 2014

MATHEMATICA

f[n_] := Table[ #^2 &[m], {m, 1, n + 1}] - FoldList[Plus, 1, 2 Array[EulerPhi, n, 2]] (* _Gregg K. Whisler_, Jun 25 2008 *)

PROG

(Haskell)

a100613 n = length [()| x <- [1..n], y <- [1..n], gcd x y > 1]

-- Reinhard Zumkeller, Jan 21 2013

(PARI) a(n) = sum(i=1, n, sum(j=1, n, gcd(i, j)>1)); \\ Michel Marcus, Jan 30 2017

CROSSREFS

Cf. A018805, A000290, A185670, A063985, A242114.

Sequence in context: A277022 A232603 A069480 * A070911 A276082 A113240

Adjacent sequences:  A100610 A100611 A100612 * A100614 A100615 A100616

KEYWORD

nonn

AUTHOR

Douglas Stones (dssto1(AT)student.monash.edu.au), Dec 02 2004

STATUS

approved

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Last modified May 21 15:00 EDT 2019. Contains 323443 sequences. (Running on oeis4.)