21865819 has 8 divisors (see below), whose sum is σ = 22679552. Its totient is φ = 21058920.

The previous prime is 21865807. The next prime is 21865829. The reversal of 21865819 is 91856812.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21865819 - 2¹¹ = 21863771 is a prime.

It is a super-2 number, since 2×21865819² = 956228081081522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21865829) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5332 + ... + 8494.

It is an arithmetic number, because the mean of its divisors is an integer number (2834944).

Almost surely, 2^21865819 is an apocalyptic number.

21865819 is a deficient number, since it is larger than the sum of its proper divisors (813733).

21865819 is a wasteful number, since it uses less digits than its factorization.

21865819 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3417.

The product of its digits is 34560, while the sum is 40.

The square root of 21865819 is about 4676.0901402775. The cubic root of 21865819 is about 279.6331036331.

The spelling of 21865819 in words is "twenty-one million, eight hundred sixty-five thousand, eight hundred nineteen".