Foias constant

In mathematical analysis, the Foias constant is a real number named after Ciprian Foias.

Evolution of the sequence for several values of , around the Foias constant. All of them lead to two accumulation points, viz. 1 and . A logarithmic scale is used.

It is defined in the following way: for every real number x1 > 0, there is a sequence defined by the recurrence relation

for n = 1, 2, 3, .... The Foias constant is the unique choice α such that if x1 = α then the sequence diverges to infinity.[1] Numerically, it is


No closed form for the constant is known.

When x1 = α then we have the limit:

where "log" denotes the natural logarithm. Consequently, one has by the prime number theorem that in this case

where π is the prime-counting function.[1]

See alsoEdit

Notes and referencesEdit

  1. ^ a b Ewing, J. and Foias, C. "An Interesting Serendipitous Real Number." In Finite versus Infinite: Contributions to an Eternal Dilemma (Ed. C. Caluse and G. Păun). London: Springer-Verlag, pp. 119–126, 2000.
  • Weisstein, Eric W. "Foias Constant". MathWorld.
  • S. R. Finch (2003). Mathematical Constants. Cambridge University Press. p. 430. ISBN 0-521-818-052. Foias constant.
  • Sloane, N. J. A. (ed.). "Sequence A085848 (Decimal expansion of Foias's Constant)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.