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A240775 The six values n in each interval [i*840, (i+1)*840), where i >= 0, for which Mordell's formulas do NOT provide a three-Egyptian-fraction solution for 4/n. 1
1, 121, 169, 289, 361, 529 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Erdős and Straus conjectured that for all integers n >= 2, the rational number 4/n can be expressed as an Egyptian fraction with exactly three unit fractions -- that is, 4/n = 1/x + 1/y + 1/z where x, y and z are positive integers. The conjecture has been verified to high values of n, and Mordell has provided formulas to compute x, y and z for many n. The values of n NOT included in Mordell's formulas are those for which n modulo 840 = {an element of this sequence}. Each element is the square of a prime.

REFERENCES

Louis J. Mordell, Diophantine Equations, Academic Press, 1967, 287-290.

LINKS

Table of n, a(n) for n=1..6.

CROSSREFS

Sequence in context: A262514 A258693 A037266 * A284643 A074730 A268519

Adjacent sequences:  A240772 A240773 A240774 * A240776 A240777 A240778

KEYWORD

nonn,fini,full

AUTHOR

Kenneth Vollmar, Apr 12 2014

STATUS

approved

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Last modified January 19 03:54 EST 2020. Contains 331031 sequences. (Running on oeis4.)