21819457 has 4 divisors (see below), whose sum is σ = 23803056. Its totient is φ = 19835860.

The previous prime is 21819437. The next prime is 21819461. The reversal of 21819457 is 75491812.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 21819457 - 2¹⁵ = 21786689 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21819437) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 991783 + ... + 991804.

It is an arithmetic number, because the mean of its divisors is an integer number (5950764).

Almost surely, 2^21819457 is an apocalyptic number.

It is an amenable number.

21819457 is a deficient number, since it is larger than the sum of its proper divisors (1983599).

21819457 is a wasteful number, since it uses less digits than its factorization.

21819457 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1983598.

The product of its digits is 20160, while the sum is 37.

The square root of 21819457 is about 4671.1301630334. The cubic root of 21819457 is about 279.4353288397.

The spelling of 21819457 in words is "twenty-one million, eight hundred nineteen thousand, four hundred fifty-seven".