OFFSET
1,5
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..118
A. N. W. Hone, Algebraic curves, integer sequences and a discrete Painlevé transcendent, arXiv:0807.2538 [nlin.SI], 2008; Proceedings of SIDE 6, Helsinki, Finland, 2004.
MAPLE
a:= proc(n) option remember;
if n < 5 then 1
else (2*a(n-1)*a(n-3) + a(n-2)^2)/a(n-4)
fi;
end proc:
seq(a(n), n = 1..30); # G. C. Greubel, Oct 08 2019
MATHEMATICA
a[n_]:= a[n]= If[n<5, 1, (2*a[n-1]a[n-3] + a[n-2]^2)/a[n-4]]; Table[a[n], {n, 30}]
RecurrenceTable[{a[1]==a[2]==a[3]==a[4]==1, a[n]==(2a[n-1]a[n-3]+ a[n-2]^2)/ a[n-4]}, a, {n, 20}] (* Harvey P. Dale, May 27 2014 *)
PROG
(PARI) my(m=30, v=concat([1, 1, 1, 1], vector(m-4))); for(n=5, m, v[n] = (2*v[n-1]*v[n-3] + v[n-2]^2)/v[n-4]); v \\ G. C. Greubel, Oct 08 2019
(Magma) [n lt 5 select 1 else (2*Self(n-1)*Self(n-3) + Self(n-2)^2)/Self(n-4): n in [1..30]]; // G. C. Greubel, Oct 08 2019
(Sage)
@CachedFunction
def a(n):
if (n<5): return 1
else: return (2*a(n-1)*a(n-3) + a(n-2)^2)/a(n-4)
[a(n) for n in (1..30)] # G. C. Greubel, Oct 08 2019
(GAP) a:=[1, 1, 1, 1];; for n in [5..30] do a[n]:=(2*a[n-1]*a[n-3] + a[n-2]^2)/a[n-4]; od; a; # G. C. Greubel, Oct 08 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Roger L. Bagula, Sep 09 2006
EXTENSIONS
Edited by N. J. A. Sloane, Sep 15 2006
More terms added by G. C. Greubel, Oct 08 2019
STATUS
approved