Density by Moduli and Lacunary Statistical Convergence
We have introduced and studied a new concept off-lacunary statistical convergence, wherefis an unbounded modulus. It is shown that, under certain conditions on a modulusf, the concepts of lacunary strong convergence with respect to a modulusfandf-lacunary statistical convergence are equivalent on bounded sequences. We further characterize thoseθfor whichSθf=Sf, whereSθfandSfdenote the sets of allf-lacunary statistically convergent sequences andf-statistically convergent sequences, respectively. A general description of inclusion between two arbitrary lacunary methods off-statistical convergence is given. Finally, we give anSθf-analog of the Cauchy criterion for convergence and a Tauberian theorem forSθf-convergence is also proved.