Call error for integers (when I haven't declared any.)

edit

I'm trying to define a pretty atrocious function (that I eventually want to solve for zeroes) in three variables, k,j,N.

I tried to just use

f=sin(2*k*2*pi/N)*sin((k+1)*2*pi/N)*sin((k-1)*2*pi/N)*sin((2*j+2)*2*pi/N)*sin^2(j*2*pi/N)*sin(6*pi/N)*sin(4*pi/N)*sin(2*pi/N)+sin(2*j*2*pi/N)*sin((j+1)*2*pi/N)*sin((j-1)*2*pi/N)*sin((2*k+2)*2*pi/N)*sin(k*2*pi/N)*sin(k*2*pi/N)*sin(6*pi/N)*sin(4*pi/N)*sin(2*pi/N)+sin((k-1)*2*pi/N)*sin((2*k+2)*2*pi/N)*sin(k*2*pi/N)*sin((2*j+2)*2*pi/N)*sin(j*2*pi/N)*sin(j*2*pi/N)*sin(12*pi/N)*sin(4*pi/N)*sin(2*pi/N)+sin((j-1)*2*pi/N)*sin((2*j+2)*2*pi/N)*sin(j*2*pi/N)*sin((2*k+2)*2*pi/N)*sin(k*2*pi/N)*sin(k*2*pi/N)*sin(12*pi/N)*sin(4*pi/N)*sin(2*pi/N)-sin((k-1)*2*pi/N)*sin((j-1)*2*pi/N)*sin((2*k+2)*2*pi/N)*sin((2*j+2)*2*pi/N)*sin(k*2*pi/N)*sin(j*2*pi/N)*sin(6*pi/N)*sin(2*pi/N)* sin(8*pi/N)-sin(12*pi/N)*sin(4*(pi/N))*sin(4*(pi/N))*sin((2*k+2)*2*pi/N)*sin((2*j+2)*2*pi/N)*sin(j*2*pi/N)*sin(j*2*pi/N)*sin(k*2*pi/N)*sin(k*2*pi/N)

but I'm getting:

TypeError: 'sage.rings.integer.Integer' object is not callable

why is this, I already had that

assume(k,'real')
assume(pi/2>k>0)
assume(j,'real')
assume(pi/2>j>0)
assume(N,'real')
assume(N>0)

so what can I do to fix this error?