A192263 a(n) = abs(a(n-1) - 3*a(n-2)) with a(1)=a(2)=1.

1, 1, 2, 1, 5, 2, 13, 7, 32, 11, 85, 52, 203, 47, 562, 421, 1265, 2, 3793, 3787, 7592, 3769, 19007, 7700, 49321, 26221, 121742, 43079, 322147, 192910, 773531, 194801, 2125792, 1541389, 4835987, 211820, 14296141, 13660681, 29227742, 11754301

Offset: 1

Author

Pasi Airikka, Jun 27 2011

Keywords

• nonn
• easy

Examples

			a(3)=abs(1-3*1)=2, a(4)=abs(2-3*1)=1, a(5)=abs(1-3*2)=5, a(6)=abs(5-3*1)=2, a(7)=abs(2-3*5)=13.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Programs

MATLAB

% n = number of computed terms of sequence. Beware of 64bit restrictions of MATLAB integers and floating point numbers
a(1)=1 ; a(2)=1 ;
for i=3:n,
   a(i) = abs(a(i-1)-3*a(i-2)) ;
end

Maple

A192263 := proc(n) option remember; if n <=2 then 1; else abs(procname(n-1)-3*procname(n-2)) ; end if; end proc: # R. J. Mathar, Jul 12 2011

Mathematica

nxt[{a_,b_}]:={b,Abs[b-3a]}; NestList[nxt,{1,1},40][[All,1]] (* Harvey P. Dale, Dec 16 2021 *)

PARI

N=66; v=vector(N); /* that many terms */
v[1]=1; v[2]=1; for(n=3,N,v[n]=abs(abs(v[n-1] - 3*v[n-2])));
v /* show terms */  /* Joerg Arndt, Jul 02 2011 */