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

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, 56, 109, 57, 241, 28, 277, 106, 137, 100, 183, 62, 395, 128, 193, 102, 489, 65, 541, 165, 203, 189, 649, 116, 551, 170, 347, 231, 829, 147, 506, 234, 434, 307, 1027, 119, 1101, 364, 450, 412, 727

Offset: 1

Author

N. J. A. Sloane, Feb 07 2011

Keywords

• nonn
• look

References

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

Links

• Alois P. Heinz, Table of n, a(n) for n = 1..10000

Crossrefs

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

Programs

Mathematica

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 *)

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