A241565 - OEIS

%I #6 Apr 25 2014 21:18:10

%S 0,0,0,0,1,3,8,15,27,38,54,71,95,119,152,186,230,277,338,404,486,571,

%T 672,777,901,1028,1175,1327,1500,1679,1881,2090,2322,2559,2822,3092,

%U 3389,3693,4026,4366,4735,5110,5515,5928,6376,6831,7322,7823,8362,8909

%N Number of 3-element subsets of {1,...,n} whose sum has more than 4 divisors.

%C If the constraint on the number of divisors is dropped, one gets A000292 = tetrahedral numbers C(n+2,3) = n*(n+1)*(n+2)/6, which therefore is an upper bound.

%C If the sums are required to have more than 3 divisors, one gets A241564.

%o (PARI) a(n,m=3,d=4)={s=0;u=vector(m,n,1)~;forvec(v=vector(m,i,[1,n]),numdiv(v*u)>d&&s++,2);s}

%K nonn

%O 1,6

%A _M. F. Hasler_, Apr 25 2014