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In the April 1975 issue of Scientific American, Martin Gardner wrote (jokingly) that Ramanujan's constant (e^(*sqrt(163))) is an integer. The name "Ramanujan's constant" was actually coined by Simon Plouffe and derives from the April Fool's joke played by Martin Gardner. The French mathematician Charles Hermite (1822-1901) observed this property of 163 long before Ramanujan's work on almost integers. [Aitken]

The largest Heegner number. [Croll]

163 = "is a prime number" by adding the letters in the alphabet code, i.e., a = 1, b = 2, c = 3, etc. [Necula]

163 is the smallest prime number that is a factor of more than one number of the form p# - 1 (163 divides both 67# - 1 and 79# - 1).

Let the cs(p) be the cumulative digit sum of all the primes 2 to p (e.g., cs(11)=2+3+5+7+1+1=19). There are the only four known primes such that cs(p)=2p; they are 5, 23, 47 and 163. [Vrba]

163 = 1 + 2 * 3^4 [Oliver-Lafont]