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A263995 Cardinality of the union of the set of sums and the set of products made from pairs of integers from {1...n}. 2

%I

%S 2,4,7,11,15,20,27,32,39,46,56,63,75,83,93,102,118,127,146,156,169,

%T 182,204,215,231,245,261,274,302,315,346,361,379,398,418,432,469,489,

%U 510,527,567,585,627,647,669,693,739,756,788,810,838,862,914,937

%N Cardinality of the union of the set of sums and the set of products made from pairs of integers from {1...n}.

%C The November 2015 - Feb 2016 round of Al Zimmermann's Programming Contests asks for sets of positive integers (instead of {1...n}) minimizing the cardinality of the union of the sum-set and the product-set for set sizes 40, 80, ..., 1000.

%D Richard K. Guy, Unsolved Problems in Number Theory, 3rd ed., Springer-Verlag New York, 2004. Problem F18.

%H Hugo Pfoertner, <a href="/A263995/b263995.txt">Table of n, a(n) for n = 1..10000</a>

%H P. Erdős and E. Szemeredi, <a href="http://renyi.hu/~p_erdos/1983-18.pdf">On sums and products of integers</a>, Studies in Pure Mathematics, Birkhäuser, Basel, 1983, pp. 213-218. DOI:10.1007/978-3-0348-5438-2_19

%H Al Zimmermann's Programming Contests, <a href="http://azspcs.com/Contest/SumsAndProducts">Sums and Products</a>, Nov 2015 - Feb 2016.

%e a(3)=7 because the union of the set of sums {1+1, 1+2, 1+3, 2+2, 2+3, 3+3) and the set of products {1*1, 1*2, 1*3, 2*2, 2*3, 3*3} = {2,3,4,5,6} U {1,2,3,4,6,9} = {1,2,3,4,5,6,9} has cardinality 7.

%Y Cf. A263996.

%K nonn

%O 1,1

%A _Hugo Pfoertner_, Nov 15 2015

%E Comment describing goal of Al Zimmermann's Programming Contest corrected by _Al Zimmermann_, Nov 24 2015

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Last modified July 18 11:37 EDT 2019. Contains 325138 sequences. (Running on oeis4.)