Legendre's Constant
The number 1.08366 in Legendre's 
guess at the Prime Number Theorem
This expression is correct to leading term only.
References
Le Lionnais, F. Les nombres remarquables. Paris: Hermann, p. 147, 1983.
Wagon, S. Mathematica in Action. New York: W. H. Freeman, pp. 28-29, 1991.
- Kolmogorov-Sinai Entropy
- Kolmogorov-Smirnov Test
- Korselt's Criterion
- Kovalevskaya Exponent
- Kozyrev-Grinberg Theory
- k-Partite Graph
- Kramers Rate
- Krawtchouk Polynomial
- Kreisel Conjecture
- Kronecker Decomposition Theorem
- Kronecker Delta
- Kronecker Product
- Kronecker's Polynomial Theorem
- Kronecker Symbol
- Krull Dimension
- Kruskal's Algorithm
- Kruskal's Tree Theorem
- KS Entropy
- k-Statistic
- k-Subset
- k-Theory
- k-Tuple Conjecture
- Kuen Surface
- Kuhn-Tucker Theorem
- Kuiper Statistic