A series of expressions to calculate the monthly median F₁ layer penetration frequency (ƒoF₁) as a function of the ionospheric index IF₂ was reported by DuCharme et al., [1971]. Using similar techniques and the same data base, development of a series of expressions to calculate ƒoF₁ as a function of the Zurich smoothed sunspot number R₁₂ is described. The derived expressions are evaluated for the period of maximum solar activity 1967 through 1969 and compared with observed ƒoF₁ data for this period, which are outside the 1954 through 1966 data base used to develop the expressions.