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 A002967 Egyptian fractions: number of solutions of 1 = 1/x_1 + ... + 1/x_n in positive integers. (Formerly M4745) 6
 1, 1, 10, 215, 12231, 2025462, 1351857641, 6255560531733 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Solutions differing only in the order of the x_i are counted as distinct. All denominators in the expansion 1 = 1/x_1 + ... + 1/x_n are bounded by A000058(n-1)=A129871(n). - Max Alekseyev, Dec 30 2003 REFERENCES Mohammad K. Azarian, Diophantine Pair, Problem B-881, Fibonacci Quarterly, Vol. 37, No. 3, August 1999, pp. 277-278.  Solution published in Vol. 38, No. 2, May 2000, pp. 183-184. R. K. Guy, Unsolved Problems in Number Theory, D11. D. Singmaster, "The number of representations of one as a sum of unit fractions," unpublished manuscript, 1972. N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Zachary Harris, Joel Louwsma, On Arithmetical Structures on Complete Graphs, arXiv:1909.02022 [math.NT], 2019. Putnam Competition, 58th Putnam Mathematical Competition, 1997, Problem A-5 D. Singmaster, The number of representations of one as a sum of unit fractions, Unpublished M.S., 1972 EXAMPLE For n=3 the 10 solutions are {2,3,6} (6 ways), {2,4,4} (3 ways), {3,3,3} (1 way). CROSSREFS Cf. A002966, A006585. Cf. A000058. Sequence in context: A213788 A278125 A274763 * A243476 A305107 A294850 Adjacent sequences:  A002964 A002965 A002966 * A002968 A002969 A002970 KEYWORD nonn,nice,hard,more AUTHOR EXTENSIONS a(7) from Jud McCranie a(8) from John Dethridge, Jan 11 2004 STATUS approved

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Last modified January 20 14:02 EST 2020. Contains 331094 sequences. (Running on oeis4.)