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 A033179 Numbers k such that exactly one multiset of k positive integers has equal sum and product. 6
 2, 3, 4, 6, 24, 114, 174, 444 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS No other terms below 10^10 (Ecker, 2002). Probably finite and complete. For any m, there is the multiset {m, 2, 1^(m-2)} with sum and product 2m. (A) If m-1 is composite (m-1=ab), then {a+1, b+1, 1^(m-2)} is another multiset with sum = product. (Hugo van der Sanden) (B) If 2m-1 is composite (2m-1=ab), then {2, (a+1)/2, (b+1)/2, 1^(m-3)} is another such multiset. (Don Reble) (C) If m = 30j+12, then {2, 2, 2, 2, 2j+1, 1^(30j+7)} is another such multiset. (Don Reble) Conditions (A), (B), (C) eliminate all k's except for 2, 3, 4, 6, 30j+0, and 30j+24. REFERENCES J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 174, p. 54, Ellipses, Paris 2008. R. K. Guy, 'Unsolved Problems in Number Theory' (Section D24). LINKS Table of n, a(n) for n=1..8. Michael W. Ecker, When Does a Sum of Positive Integers Equal Their Product? Mathematics Magazine 75(1), 2002, pp. 41-47. Piotr Miska and Maciej Ulas, On the Diophantine equation sigma_2(Xn)=sigma_n(Xn), arXiv:2203.03942 [math.NT], 2022. Michael A. Nyblom, Sophie Germain Primes and the Exceptional Values of the Equal-Sum-And-Product Problem, Fib. Q. 50(1), 2012, 58-61. CROSSREFS Cf. A033178. Sequence in context: A217442 A065199 A249156 * A067244 A084811 A051856 Adjacent sequences: A033176 A033177 A033178 * A033180 A033181 A033182 KEYWORD nonn,more AUTHOR David W. Wilson EXTENSIONS Revised by Don Reble, Jun 11 2005 Edited by Max Alekseyev, Nov 13 2013 STATUS approved

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Last modified May 18 09:54 EDT 2024. Contains 372620 sequences. (Running on oeis4.)