A082986 Largest x such that 1/x + 1/y + 1/z = 1/n.
6, 42, 156, 420, 930, 1806, 3192, 5256, 8190, 12210, 17556, 24492, 33306, 44310, 57840, 74256, 93942, 117306, 144780, 176820, 213906, 256542, 305256, 360600, 423150, 493506, 572292, 660156, 757770, 865830, 985056, 1116192, 1260006, 1417290, 1588860, 1775556
Offset: 1
Links
- Charles R Greathouse IV, Table of n, a(n) for n = 1..5000
Programs
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Mathematica
a[n_] := Module[{f, d, t, x = 0}, For[z = n+1, z <= Quotient[201*n, 100], z++, f = 1/n - 1/z; d = Denominator[f]; Do[t = (y/d + 1/y)/f; If[Denominator[t] == 1, x = Max[x, t*y]], {y, Divisors[d]}]]; x]; Table[a[n], {n, 1, 36}] (* Jean-François Alcover, Jul 10 2017, after Charles R Greathouse IV *) -
PARI
a(n)=my(f, d, t, x); for(z=n+1, 201*n\100, f=1/n-1/z; d=denominator(f); fordiv(d, y, t=(y/d+1/y)/f; if(denominator(t)==1, x=max(x, t*y)))); x \\ Charles R Greathouse IV, Oct 17 2012
Formula
a(n) >= n^4 + 2n^3 + 2n^2 + n (cf. A169938). - Charles R Greathouse IV, Oct 17 2012. [Note this is at present only a lower bound! - N. J. A. Sloane, Jan 27 2014]
a(n) < 3*n^4 for n>=2 (upper bound). - Carmine Suriano, Feb 20 2014
Extensions
a(6)-a(36) from Charles R Greathouse IV, Oct 17 2012
Deleted incorrect (or at least unproved) Mma program. - N. J. A. Sloane, Jan 27 2014
Comments