“…The problem of estimating coefficients |a n |, n ≥ 2 is still open. However, a lot of results for |a 2 |, |a 3 | and |a 4 | were proved for some subclasses of σ (see [3], [5], [9], [11], [21], [23], [24], [26], [27]). Unfortunatelly, none of them are not sharp.…”