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A085349
Ratio-determined insertion sequence I(0.26688) (see the link below).
2
1, 4, 15, 71, 269, 1274, 4827, 22861, 86617, 410224, 1554279, 7361171, 27890405, 132090854, 500473011, 2370274201, 8980623793, 42532844764, 161150755263, 763220931551, 2891732970941, 13695443923154, 51890042721675
OFFSET
1,2
COMMENTS
This is one of the "twin" ratio-determined insertion sequences (RDIS) that are "children" in the next generation below the "parent" sequences I(0.25024) (A004253) and I(0.26816) (A001353) in the recurrence tree of RDIS sequences. The RDIS twin of this sequence is A085348. See the link for an explanation of RDIS twin. See A082630 or A082981 for other recent examples of RDIS sequences.
FORMULA
It appears that a(n)=18a(n-2)-a(n-4).
Apparently a(n)a(n+3) = 11 + a(n+1)a(n+2). - Ralf Stephan, May 29 2004
MATHEMATICA
LinearRecurrence[{0, 18, 0, -1}, {1, 4, 15, 71}, 30] (* Harvey P. Dale, Mar 04 2013 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
John W. Layman, Jun 24 2003
STATUS
approved