OFFSET
0,1
COMMENTS
It seems that degrees of factors when using [2,1,1,y] as initial condition are given by A233522. - F. Chapoton, May 21 2020
It seems also that degrees (w.r.t. x) of factors when using [2,1,x,y] as initial condition are given by A247907. - F. Chapoton, Jan 03 2021
Somos conjectures that log(a(n)) ~ 1.25255*c^n, where c = A060006. - Bill McEachen, Oct 11 2022
LINKS
Robert Israel, Table of n, a(n) for n = 0..26
Math Stack Exchange, Is OEIS A248049 an Integer Sequence
FORMULA
a(n) = a(4-n) for all n in Z.
a(n) * a(n+4) = (a(n+1) + a(n+2)) * (a(n+2) + a(n+3)) for all n in Z.
MAPLE
a[0]:= 2: a[1]:= 1: a[2]:= 1: a[3]:= 1:
for n from 4 to 20 do
a[n] := (a[n-1] + a[n-2]) * (a[n-2] + a[n-3]) / a[n-4]
od:
seq(a[i], i=0..20); # Robert Israel, Mar 18 2020
PROG
(PARI) {a(n) = if( n<0, n=4-n); if( n<4, (n==0)+1, (a(n-1) + a(n-2)) * (a(n-2) + a(n-3)) / a(n-4))};
CROSSREFS
KEYWORD
nonn
AUTHOR
Michael Somos, Sep 30 2014
STATUS
approved