Question 743007
Given 
{{{ a[0] = 0 }}}
{{{ a[1]=3 }}} 
{{{ a[n]=a[n-1]-a[n-2] }}}

Thus
{{{ a[2] = a[1] - a[0] = 3 - 0 = 3 }}}
{{{ a[3] = a[2] - a[1] = 3 - 3 = 0 }}}
{{{ a[4] = a[3] - a[2] = 0 - 3 = -3 }}}