  Superconductivity in small metallic specimens is studied with regard to the
size dependence of the "parity gap" (Delta_P), a parameter distinguishing
between the energy of even and odd number of electrons in the granule. Delta_P
is shown to be an increasing function of level spacing delta. The energy gap of
superconductor Delta, on the other hand, decreases with increasing delta and
vanishes at delta=delta_c which is of the order of Delta. However, nonzero
value of Delta_P persists above delta_c in a "gapless"
superconducting-insulating state. Level degeneracy in small specimens having
perfect geometry changes the size dependence of the parity gap, the Josephson
effect, and flux quantization. Parity gap is evaluated using an interpolation
procedure between the continuum limit (delta<<Delta), the moderate mesoscopic
regime (delta ~ Delta), and the nanoscopic scale (delta>>Delta), for which an
exact solution to the pairing problem is provided with the numeric
diagonalization of system Hamiltonian in a small metallic cluster.
