  The correlation coefficients of the linear regression of six solar indices
versus F10,7 were analyzed in solar cycles 21, 22 and 23. We also analyzed the
interconnection between these indices and F10,7 with help of the approximation
by the polynomials of second order. The indices we've studied in this paper
are: Wolf numbers - W, 530,3 nm coronal line flux - F530, the total solar
irradiance - TSI, Mg II UV-index 280 nm core-to-wing ratio, Flare Index - FI
and Counts of flares. In the most cases the regressions of these solar indices
versus F10,7 are close to linear except the moments of time near to the
minimums and maximums of 11-year activity. For the linear regressions we found
that the values of correlation coefficients Kcorr(t) for the indices versus
F10,7 and W show the cyclic variations with periods approximately equal to the
to half length of 11-year cycle - 5,5 years approximately.
