

A241565


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


0



0, 0, 0, 0, 1, 3, 8, 15, 27, 38, 54, 71, 95, 119, 152, 186, 230, 277, 338, 404, 486, 571, 672, 777, 901, 1028, 1175, 1327, 1500, 1679, 1881, 2090, 2322, 2559, 2822, 3092, 3389, 3693, 4026, 4366, 4735, 5110, 5515, 5928, 6376, 6831, 7322, 7823, 8362, 8909
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OFFSET

1,6


COMMENTS

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


LINKS



PROG

(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}


CROSSREFS



KEYWORD

nonn


AUTHOR



STATUS

approved



