The paper devoted the memory of the outstanding Russian mathematician A. F. Leont'ev (1917–1987) consists of three sections. In § 1 the author sets one probably new hypothesis concerning the well known Riemann's Zeta Function $\zeta(z)$ and proves with the helps of this hypothesis that all zeros of $\zeta(z)$ are simple and lie only on the real axis and on the line $\Re z=1/2$. In § 2 the formulation of one theorem on convex functions from the first part of the monography of Hayman W. K. and Kennedy P. B. a bit is slightly corrected. In the last section the author express his gratitude to some mathematicians (especially to A. F. Leont'ev) who supported him throughout his comparatively long scientific career.