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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 ErdÅ‘s 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 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 June 21 19:59 EDT 2021. Contains 345365 sequences. (Running on oeis4.)