Voozh

A240807

a(0)=a(1)=-1, a(2)=2; thereafter a(n) = a(n-1-a(n-1))+a(n-2-a(n-2)) unless a(n-1) <= n-1 or a(n-2) <= n-2 in which case the sequence terminates.

-1, -1, 2, 1, 1, 3, 3, 3, 2, 4, 6, 4, 4, 5, 4, 8, 9, 6, 7, 8, 8, 8, 9, 10, 10, 9, 13, 14, 10, 12, 13, 12, 14, 15, 14, 15, 16, 16, 16, 17, 18, 18, 19, 20, 20, 20, 19, 23, 24, 20, 22, 22, 22, 25, 23, 22, 27, 27, 25, 28, 27, 27, 29, 29, 29, 29, 31, 31, 31, 32, 32, 32, 33, 34, 34, 35, 36, 36, 36, 37, 38, 38, 39, 40, 40, 40, 40, 39, 43, 44, 40, 42, 42, 42

(list; graph; refs; listen; history; text; internal format)

OFFSET

0,3

REFERENCES

Higham, Jeff and Tanny, Stephen, A tamely chaotic meta-Fibonacci sequence. Twenty-third Manitoba Conference on Numerical Mathematics and Computing (Winnipeg, MB, 1993). Congr. Numer. 99 (1994), 67-94.

LINKS

N. J. A. Sloane, Table of n, a(n) for n = 0..20000

Index entries for Hofstadter-type sequences

MAPLE

a:=proc(n) option remember;

if n = 0 then -1

elif n = 1 then -1

elif n = 2 then 2

else

if (a(n-1) <= n-1) and (a(n-2) <= n-2) then

a(n-1-a(n-1))+a(n-2-a(n-2));

else lprint("died with n =", n); return (-1);