%I #13 Mar 18 2014 17:44:06

%S 1,2,3,3,4,4,4,5,5,5,6,6,6,6,7,7,7,7,7,8,8,8,8,8,8,9,9,9,9,9,10,10,10,

%T 10,10,10,10,10

%N Size of smallest set S of integers such that {0,1,2,...,n} is a subset of S-S, where S-S={abs(i-j) | i,j in S}.

%C S need not be a subset of {0,1,2,...,n}, unlike the definition in A046693.

%D J. Leech, On the representation of 1,2,...,n by differences, J. London Math. Soc. 31 (1956) 160-169.

%e a(18)=7 since all integers in {0,1,2...18} are differences of elements of {0,6,9,10,17,22,24}, but not of any 6-element set.

%e In other words, {0,6,9,10,17,22,24} is an unrestricted difference basis w.r.t. A005488(7)=18.

%Y A005488, A046693

%K nonn

%O 0,2

%A _Steven Finch_, Mar 18 2014