  We introduce two sequences of two-variable polynomials $\{ L^n_K (t,
\ell)\}_{n=1}^{\infty}$ and $\{ F^n_K (t, \ell)\}_{n=1}^{\infty}$, expressed in
terms of index value of a crossing and $n$-dwrithe value of a virtual knot $K$,
where $t$ and $\ell$ are variables. Basing on the fact that $n$-dwrithe is a
flat virtual knot invariant we prove that $L^n_K$ and $F^n_K$ are virtual knot
invariants containing Kauffman affine index polynomial as a particular case.
Using $L^n_K$ we give sufficient conditions when virtual knot does not admit
cosmetic crossing change.
