OFFSET
1,2
COMMENTS
(1) It appears that {a(n+1)-2a(n)} is eventually periodic, with values {2,-1,-1,-4,5,-1,-4,5,-1,-4,5,-1,-4,...}.
(2) See A139218 for the corresponding sequence using integers of the form 3k+2.
(3) M. F. Hasler, in a SeqFan memo dated Apr 09 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.
FORMULA
It appears that a(n)=a(n-1)+a(n-2)+2a(n-3), for n>4.
CROSSREFS
KEYWORD
nonn
AUTHOR
John W. Layman, Apr 11 2008
STATUS
approved