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A301989
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a(n) is the number of ways to write n as i * j * k where 2 <= i <= sqrt(n), i < j <= min(2 * i - 1, floor(n / i)), k >= 1.
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3
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0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 2, 0, 0, 1, 0, 0, 1, 0, 1, 0, 0, 0, 3, 0, 0, 0, 1, 0, 3, 0, 0, 0, 0, 1, 2, 0, 0, 0, 2, 0, 2, 0, 0, 2, 0, 0, 4, 0, 0, 0, 0, 0, 2, 0, 2, 0, 0, 0, 6, 0, 0, 1, 0, 0, 2, 0, 0, 0, 2, 0, 4, 0, 0, 1, 0, 1, 1, 0, 3, 0, 0, 0, 5, 0, 0, 0
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OFFSET
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1,12
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COMMENTS
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LINKS
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MAPLE
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N:= 100: # to get a(1)..a(N)
V:= Vector(N):
for i from 1 to isqrt(N-1) do
for j from i+1 to min(floor(N/i), 2*i-1) do
for k from 1 to floor(N/(i*j)) do
n:= i*j*k;
V[n]:= V[n]+1;
od od od:
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MATHEMATICA
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M = 100;
V = Table[0, {M}];
For[i = 1, i <= Sqrt[M-1], i++,
For[j = i+1, j <= Min[Floor[M/i], 2i-1], j++,
For[k = 1, k <= Floor[M/(i j)], k++,
n = i j k;
V[[n]] = V[[n]]+1;
]]];
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PROG
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(PARI) upto(n) = {my(res = vector(n)); for(i = 2, sqrtint(n), for(j = i+1, min(2 * i - 1, n \ i), for(k = 1, n \ (i * j), res[i*j*k]++))); res}
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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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