A118825 Numerators of the convergents of the 2-adic continued fraction of zero given by A118824.

-2, -1, 0, -1, 2, 1, 0, 1, -2, -1, 0, -1, 2, 1, 0, 1, -2, -1, 0, -1, 2, 1, 0, 1, -2, -1, 0, -1, 2, 1, 0, 1, -2, -1, 0, -1, 2, 1, 0, 1, -2, -1, 0, -1, 2, 1, 0, 1, -2, -1, 0, -1, 2, 1, 0, 1, -2, -1, 0, -1, 2, 1, 0, 1, -2, -1, 0, -1, 2, 1, 0, 1, -2, -1, 0, -1, 2, 1

Offset: 1

Author

Paul D. Hanna, May 01 2006

Keywords

• frac
• sign
• easy

Examples

			For n>=1, convergents A118825(k)/A118826(k) are:
  at k = 4*n: 1/A080277(n);
  at k = 4*n+1: 2/(2*A080277(n)-1);
  at k = 4*n+2: 1/(A080277(n)-1);
  at k = 4*n-1: 0/(-1)^n.
Convergents begin:
  -2/1, -1/1, 0/-1, -1/-1, 2/1, 1/0, 0/1, 1/4,
  -2/-7, -1/-3, 0/-1, -1/-5, 2/9, 1/4, 0/1, 1/12,
  -2/-23, -1/-11, 0/-1, -1/-13, 2/25, 1/12, 0/1, 1/16,
  -2/-31, -1/-15, 0/-1, -1/-17, 2/33, 1/16, 0/1, 1/32, ...
		

Links

• Index entries for linear recurrences with constant coefficients, signature (0,0,0,-1).

Crossrefs

Cf. A118824 (partial quotients), A118826 (denominators), A118822, A230075 (start with a(5)).

Programs

Maple

A118825:=n->sqrt((n+1)^2 mod 8))*(-1)^floor((n+3)/4); seq(A118825(n), n=1..100); # Wesley Ivan Hurt, Jan 04 2014

Mathematica

Table[Sqrt[Mod[(n+1)^2, 8]](-1)^Floor[(n+3)/4], {n, 100}] (* Wesley Ivan Hurt, Jan 04 2014 *)
PadRight[{},120,{-2,-1,0,-1,2,1,0,1}] (* Harvey P. Dale, May 26 2020 *)

PARI

{a(n)=local(p=-2,q=+1,v=vector(n,i,if(i%2==1,p,q*2^valuation(i/2,2)))); contfracpnqn(v)[1,1]}

Formula

Period 8 sequence: [ -2,-1,0,-1,2,1,0,1].

G.f.: -x*(1+x)*(x^2-x+2) / ( 1+x^4 ).

a(n) = sqrt((n+1)^2 mod 8)*(-1)^floor((n+3)/4). - Wesley Ivan Hurt, Jan 04 2014