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 A301989 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. 3
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,12 COMMENTS a(n) > 0 implies n is in A005279. LINKS Robert Israel, Table of n, a(n) for n = 1..10000 MAPLE 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: convert(V, list); # Robert Israel, Apr 04 2018 MATHEMATICA 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; ]]]; V (* Jean-François Alcover, Apr 29 2019, after Robert Israel *) PROG (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} CROSSREFS Cf. A005279. Sequence in context: A291749 A253786 A078595 * A216513 A291437 A302231 Adjacent sequences:  A301986 A301987 A301988 * A301990 A301991 A301992 KEYWORD nonn AUTHOR David A. Corneth, Mar 30 2018 STATUS approved

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Last modified December 2 05:03 EST 2020. Contains 338865 sequences. (Running on oeis4.)