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A100448 Number of triples (i,j,k) with 1 <= i <= j < k <= n and GCD{i,j,k} = 1. 15
0, 1, 4, 9, 19, 30, 51, 73, 106, 140, 195, 241, 319, 388, 480, 572, 708, 813, 984, 1124, 1310, 1485, 1738, 1926, 2216, 2462, 2777, 3059, 3465, 3749, 4214, 4590, 5060, 5484, 6048, 6474, 7140, 7671, 8331, 8899, 9719, 10289, 11192, 11902, 12754, 13535, 14616 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Probably the partial sums of A102309. - Ralf Stephan, Jan 03 2005

LINKS

R. J. Mathar, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = (A071778(n)-1)/6. - Vladeta Jovovic, Nov 30 2004

(1/6) {-1 + sum[k=1..n, moebius(k)*floor(n/k)^3 ]. - Ralf Stephan, Jan 03 2005

MAPLE

f:=proc(n) local i, j, k, t1, t2, t3; t1:=0; for i from 1 to n do for j from i to n do t2:=gcd(i, j); for k from j+1 to n do t3:=gcd(t2, k); if t3 = 1 then t1:=t1+1; fi; od: od: od: t1; end;

MATHEMATICA

f[n_] := Length[ Union[ Flatten[ Table[ If[ GCD[i, j, k] == 1, {i, j, k}], {i, n}, {j, i, n}, {k, j + 1, n}], 2]]]; Table[ If[n > 3, f[n] - 1, f[n]], {n, 47}] (* Robert G. Wilson v, Dec 14 2004 *)

CROSSREFS

Cf. A015616, A015631, A027430, A071778, A018805.

Sequence in context: A184723 A075649 A199972 * A059820 A180784 A015618

Adjacent sequences:  A100445 A100446 A100447 * A100449 A100450 A100451

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane, Nov 21 2004

EXTENSIONS

More terms from Robert G. Wilson v, Dec 14 2004

Edited by N. J. A. Sloane, Sep 06 2008 at the suggestion of R. J. Mathar

STATUS

approved

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Last modified March 22 22:05 EDT 2017. Contains 283901 sequences.