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COMMENTS
| (1) It appears that {a(n+1)-2a(n)} is eventually periodic, with values {1,-2,-2,-5,-5,10,-5,-5,10,-5,-5,10,-5,...}.
(2) See A139217 for the corresponding sequence using integers of the form 3k+1.
(3) Maximilian Hasler, in a SeqFan memo dated Apr. 9, 2008, notes that the Jacobsthal sequence (A001045) from a(2) on (i.e., 1,3,5,11,21,...) gives the smallest positive odd integer such that all subsets of {a(2),...,a(n)} have a different sum.
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