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A241563
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Number of 3-element subsets of {1,...,n} whose sum has more than 2 divisors.
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2
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0, 0, 1, 3, 8, 14, 25, 38, 58, 83, 118, 158, 210, 268, 339, 417, 510, 611, 728, 855, 1001, 1158, 1337, 1529, 1745, 1973, 2227, 2495, 2789, 3098, 3436, 3792, 4180, 4587, 5028, 5488, 5984, 6500, 7053, 7627, 8241, 8880, 9562, 10270, 11022, 11802, 12627, 13478
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OFFSET
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1,4
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COMMENTS
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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.
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LINKS
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PROG
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(PARI) a(n, m=3, d=2)={s=0; u=vector(m, n, 1)~; forvec(v=vector(m, i, [1, n]), numdiv(v*u)>d&&s++, 2); s}
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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