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A227610 Number of ways 1/n can be expressed as the sum of three distinct unit fractions: 1/n = 1/x + 1/y + 1/z satisfying 0 < x < y < z. 9
1, 6, 15, 22, 30, 45, 36, 62, 69, 84, 56, 142, 53, 124, 178, 118, 67, 191, 74, 274, 227, 145, 87, 342, 146, 162, 216, 322, 100, 461, 84, 257, 304, 199, 435, 508, 79, 204, 360, 580, 115, 587, 98, 455, 618, 192, 129, 676, 217, 417, 369, 449, 119, 573, 543, 759, 367, 240, 166, 1236, 102, 261, 857, 428, 568, 717, 115, 537, 460, 1018, 155, 1126, 112, 276, 839 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

See A073101 for the 4/n conjecture due to Erdős and Straus.

LINKS

Jud McCranie, Table of n, a(n) for n = 1..500

Christian Elsholtz, Sums Of k Unit Fractions, Trans. Amer. Math. Soc. 353 (2001), 3209-3227.

David Eppstein, Algorithms for Egyptian Fractions

David Eppstein, Ten Algorithms for Egyptian Fractions, Wolfram Library Archive.

Ron Knott, Egyptian Fractions

Eric Weisstein's World of Mathematics, Egyptian Fraction

Index entries for sequences related to Egyptian fractions

EXAMPLE

a(1)=1 because 1 = 1/2 + 1/3 + 1/6;

a(2)=6 because 1/2 = 1/3 + 1/7 + 1/42 = 1/3 + 1/8 + 1/24 = 1/3 + 1/9 + 1/18 = 1/3 + 1/10 + 1/15 = 1/4 + 1/5 + 1/20 = 1/4 + 1/6 + 1/12;

a(3)=15 because 1/3 = 1/x + 1/y + 1/z presented as {x,y,z}: {4,13,156}, {4,14,84}, {4,15,60}, {4,16,48}, {4,18,36}, {4,20,30}, {4,21,28}, {5,8,120}, {5,9,45}, {5,10,30}, {5,12,20}, {6,7,42}, {6,8,24}, {6,9,18}, {6,10,15}; etc.

MATHEMATICA

f[n_] := Length@ Solve[1/n == 1/x + 1/y + 1/z && 0 < x < y < z, {x, y, z}, Integers]; Array[f, 70]

CROSSREFS

Cf. A002966, A073546.

Cf. A227611 (2/n), A075785 (3/n), A073101 (4/n), A075248 (5/n), A227612.

Cf. A347566, A347569.

Sequence in context: A130178 A100410 A095032 * A238905 A187918 A190747

Adjacent sequences:  A227607 A227608 A227609 * A227611 A227612 A227613

KEYWORD

nonn

AUTHOR

Robert G. Wilson v, Jul 17 2013

STATUS

approved

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Last modified January 20 10:09 EST 2022. Contains 350471 sequences. (Running on oeis4.)