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Almost All


Almost all positive integers have a property P if the natural density of the set satisfying P is 1. If A(x) counts the positive integers not exceeding x that satisfy P, this means A(x)∼x as x->infty. Equivalently, the number of exceptions not exceeding x is o(x), where o(x) is one of the Landau symbols of asymptotic notation.

For example, almost all positive integers are composite numbers (which is not in conflict with the second of Euclid's theorems that there are an infinite number of primes).

As another example, in any fixed integer base b>=2, almost all positive integers contain any specified digit in their base-b representation. The decimal digit 3 is an illustrative case (Numberphile 2012).


See also

Almost Surely, Asymptotic Notation, For All, Landau Symbols, Normal Order

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References

Hardy, G. H. Ramanujan: Twelve Lectures on Subjects Suggested by His Life and Work, 3rd ed. New York: Chelsea, p. 50, 1999.Hardy, G. H. and Wright, E. M. An Introduction to the Theory of Numbers, 5th ed. Oxford, England: Clarendon Press, p. 8, 1979.Numberphile. "3 Is Everywhere." Apr. 1, 2012. https://www.youtube.com/watch?v=UfEiJJGv4CE.

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Almost All

Cite this as:

Weisstein, Eric W. "Almost All." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/AlmostAll.html

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