A007449 a(0) = 7, a(1) = 9; for n >= 0, a(2n+1) = a(2n-1)^2 - a(2n-2), a(2n+2) = a(2n)^2 - a(2n+1). (Formerly M4337)

7, 9, 40, 74, 1526, 5436, 2323240, 29548570, 5397414549030, 873117986721660, 29132083813207600287219240, 762335018736884842676898606570, 848678307299752276902028307632840866100214927571030

Offset

0,1

References

Intelligence test in Chess Life, Vol. 49(#6) 1994, p. 14.

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

Robert G. Wilson v, Table of n, a(n) for n = 0..21

Formula

a(n+1) = a(n-1)^2 - a(n - 2*(1 - n mod 2)), a(0)=7, a(1)=9. - Reinhard Zumkeller, Mar 25 2003

Mathematica

a[n_] := a[n - 2]^2 - a[n - 3 + If[ EvenQ@ n, 2, 0]]; a[0] = 7; a[1] = 9; Array[a, 14, 0] (* Robert G. Wilson v, Aug 30 2014 *)

Prog

(PARI) a(n)=if(n<0, 0, if(n<2, [7, 9][n+1], a(n-2)^2-a(n-2+(-1)^n)))

Crossrefs

Sequence in context: A140787 A032695 A323676 * A189053 A067649 A025631

Adjacent sequences: A007446 A007447 A007448 * A007450 A007451 A007452

Keyword

nonn,easy

Author

N. J. A. Sloane

Extensions

More terms from Reinhard Zumkeller, Mar 25 2003

Status

approved