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%I #3 Mar 30 2012 17:22:33
%S 3,7,8,9,13,15,18,19,20,21,23,26,27,28,31,33,37,38,43,44,45,46,48,49,
%T 51,53,55,56,57,58,59,60,62,63,68,69,72,73,75,77,78,79,80,83,85,87,88,
%U 91,92,93,94,97,98,99,102,103,108,110,111,113,115,117,118,121,123,124,128
%N Numbers n such that there are integers a < b with a+(a+1)+...+(n-1) = n+(n+1)+...+b.
%e 7 is in this sequence because 4+5+6 = 7+8.
%t lst={}; Do[i1=n-1; i2=n; s1=i1; s2=i2; While[i1>1 && s1!=s2, If[s1<s2, i1--; s1=s1+i1, i2++; s2=s2+i2]]; If[s1==s2, AppendTo[lst, n]], {n, 2, 140}]; lst
%Y Cf. A094550, A094552, A094553.
%K nonn
%O 1,1
%A _T. D. Noe_, May 10 2004
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