successions de recurrencia

a_{n} = a_{n+(-1)}+(-1)·a_{n+(-2)}

a_{6k+1} = a

a_{6k+2} = b

a_{6k+3} = b+(-a)

a_{6k+4} = (-a)

a_{6k+5} = (-b)

a_{6k+6} = (-b)+a

a_{n} = ( a_{n+(-1)}/a_{n+(-2)} )

a_{6k+1} = a

a_{6k+2} = b

a_{6k+3} = (b/a)

a_{6k+4} = (1/a)

a_{6k+5} = (1/b)

a_{6k+6} = (a/b)