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A185953 Number of pairwise coprime triples of positive integers with largest element n (i.e., A015617(n) - A015617(n-1)). 6

%I #28 Mar 05 2019 04:58:07

%S 0,0,1,1,5,1,11,6,12,5,31,6,45,14,21,24,79,15,101,27,49,37,149,28,126,

%T 56,109,57,241,28,277,106,137,100,183,62,395,128,193,102,489,65,541,

%U 165,203,189,649,116,551,170,347,231,829,147,506,234,434,307,1027,119,1101,364,450,412,727

%N Number of pairwise coprime triples of positive integers with largest element n (i.e., A015617(n) - A015617(n-1)).

%D Robert Israel, Posting to Sequence Fans Mailing List, Feb 06, 2011

%H Alois P. Heinz, <a href="/A185953/b185953.txt">Table of n, a(n) for n = 1..10000</a>

%t a[n_] := Sum[Boole[GCD[a, n] == 1 && GCD[b, n] == 1 && GCD[a, b] == 1], {a, 1, n-2}, {b, a+1, n-1}]; Array[a, 100] (* _Jean-François Alcover_, Mar 05 2019, from PARI *)

%o (PARI) a(n)=sum(a=1,n-2,sum(b=a+1,n-1,gcd(a,n)==1&&gcd(b,n)==1&&gcd(a,b)==1)) \\ _Charles R Greathouse IV_, Apr 28 2015

%Y Cf. A015617. Row sums of triangle A186230. Column 3 of triangle A186972.

%K nonn,look

%O 1,5

%A _N. J. A. Sloane_, Feb 07 2011

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Last modified March 28 18:04 EDT 2024. Contains 371254 sequences. (Running on oeis4.)