

A248049


a(n) = (a(n1) + a(n2)) * (a(n2) + a(n3)) / a(n4) with a(0) = 2, a(1) = a(2) = a(3) = 1.


2



2, 1, 1, 1, 2, 6, 24, 240, 3960, 184800, 33033000, 26125799700, 219429008298500, 31064340573760168675, 206377779224083011749949745, 245390990689739612867279321757020455, 230795626149641527446533813473152766756062242744
(list;
graph;
refs;
listen;
history;
text;
internal format)



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


LINKS



FORMULA

a(n) = a(4n) 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[n1] + a[n2]) * (a[n2] + a[n3]) / a[n4]
od:


PROG

(PARI) {a(n) = if( n<0, n=4n); if( n<4, (n==0)+1, (a(n1) + a(n2)) * (a(n2) + a(n3)) / a(n4))};


CROSSREFS



KEYWORD

nonn


AUTHOR



STATUS

approved



