A086882 a(n) is the period of the imaginary continued fraction expansion of sqrt(-n).

0, 0, 2, 2, 0, 4, 4, 5, 4, 0, 6, 6, 6, 10, 8, 6, 0, 8, 8, 10, 8, 10, 12, 11, 8, 0, 10, 10, 12, 16, 10, 17, 11, 12, 14, 10, 0, 12, 12, 12, 12, 16, 12, 16, 16, 16, 26, 17, 12, 0, 14, 14, 16, 22, 16, 16, 14, 16, 20, 18, 16, 36, 20, 14, 0, 16, 16, 22, 16, 26, 18, 27, 16, 30, 20, 17, 26, 22

Offset

0,3

Comments

Numbers n for which a(n) is odd seem to be a subset of numbers n for which A003285(n) is a multiple of 4. - Thomas Baruchel, Jul 03 2007

Links

Table of n, a(n) for n=0..77.

Example

a(7) = 5 because sqrt(-7) = [2i, -2i, {-3i, -2i, -2i, -2i, -3i},...].

Prog

(PARI) complex_period(n)= { local(a, b, c, d, k, oa, oc, i, s); s=sqrtint(n); if(issquare(c=n), 0, until(c==oc, oc=c; oa=a; if((a = (n-b^2)/c) == oa, return(2*i)); i += (k = (s-b)\a); d = a*k+b; c = (n-d^2)/a; b = (s+d)%c-s); 2*i-k); }

Crossrefs

Cf. A003285.

Sequence in context: A307076 A342472 A308720 * A341415 A328141 A168587

Adjacent sequences: A086879 A086880 A086881 * A086883 A086884 A086885

Keyword

easy,nonn

Author

Thomas Baruchel, Aug 22 2003

Extensions

Edited by Don Reble, Jul 31 2006

Status

approved