OFFSET
0,2
COMMENTS
Hankel transform of A184018.
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..75
Paul Barry, On Motzkin-Schröder Paths, Riordan Arrays, and Somos-4 Sequences, J. Int. Seq. (2023) Vol. 26, Art. 23.4.7.
FORMULA
a(n) = (9*a(n-1)*a(n-3) - 5*a(n-2)^2)/a(n-4).
MATHEMATICA
a[n_] := a[n] = (9 a[n - 1] a[n - 3] - 5 a[n - 2]^2)/a[n - 4]; a[0] = 1; a[1] = 2; a[2] = 13; a[3] = 97; Array[a, 17, 0]
RecurrenceTable[{a[0]==1, a[1]==2, a[2]==13, a[3]==97, a[n]==(9a[n-1]a[n-3]- 5a[n-2]^2)/a[n-4]}, a[n], {n, 20}] (* Harvey P. Dale, Sep 06 2011 *)
PROG
(Magma) I:=[901, 29186, 1647721, 93837697]; [1, 2, 13, 97] cat [n le 4 select I[n] else (9*Self(n-1)*Self(n-3) - 5*Self(n-2)^2)/Self(n-4): n in [1..30]]; // G. C. Greubel, Aug 14 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul Barry, Jan 08 2011
STATUS
approved