A141520 a(1) = 0, a(2) = a(3) = 1; a(n) = a(n-1)*a(n-2) + a(n-2)*a(n-3) for n > 3.

0, 1, 1, 1, 2, 3, 8, 30, 264, 8160, 2162160, 17645379840, 38152152118080000, 673209215875134265982054400, 25684380411361480419900838705211915059200000

Offset

1,5

References

Martin Gardner, Mathematical Circus, Random House, New York, 1981, p. 165.

Links

Michael De Vlieger, Table of n, a(n) for n = 1..21

Mathematica

t={0, 1, 1}; Do[AppendTo[t, t[[-3]]*t[[-2]]+t[[-2]]*t[[-1]]], {n, 13}]; t (* Vladimir Joseph Stephan Orlovsky, Feb 03 2012 *)
Nest[Append[#, #[[-1]] #[[-2]] + #[[-2]] #[[-3]]] &, {0, 1, 1}, 12] (* Michael De Vlieger, Dec 17 2017 *)
RecurrenceTable[{a[1]==0, a[2]==a[3]==1, a[n]==a[n-1]a[n-2]+a[n-2]a[n-3]}, a, {n, 15}] (* Harvey P. Dale, Oct 04 2020 *)

Prog

(MATLAB)
function y=fib(n)
%Generates running geometric numbers
fz(1)=0; fz(2)=1; fz(3)=1;
for k=4:n
fz(k)=fz(k-2)*(fz(k-1)+fz(k-3));
end
y=fz(n);

Crossrefs

Sequence in context: A053556 A301737 A001048 * A072042 A160586 A340935

Adjacent sequences: A141517 A141518 A141519 * A141521 A141522 A141523

Keyword

nonn

Author

Matt Wynne (matwyn(AT)verizon.net), Aug 11 2008

Status

approved