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%I #4 Mar 30 2012 17:37:52
%S 1,2,2,3,3,3,4,4,4,5,5,5,5,6,6,6,6,7,7,7,7,7,8,8,8,8,8
%N a(n) is the cardinality of the smallest subset S1 of S={1,2,3,...,n} such that every element of S is either in S1 or is the sum of two elements of S1.
%e a(6)=3 since, for S1={1,2,4}, we have 1=1, 2=2, 3=1+2, 4=4, 5=1+4 and 6=2+4 and no set S1 with fewer than three elements has the required property.
%K nonn
%O 1,2
%A _John W. Layman_, Apr 24 2003
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