21820638 has 16 divisors (see below), whose sum is σ = 49875840. Its totient is φ = 6234456.

The previous prime is 21820633. The next prime is 21820661. The reversal of 21820638 is 83602812.

It is a super-2 number, since 2×21820638² = 952280485454088, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21820633) 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, 259728 + ... + 259811.

It is an arithmetic number, because the mean of its divisors is an integer number (3117240).

Almost surely, 2^21820638 is an apocalyptic number.

21820638 is an abundant number, since it is smaller than the sum of its proper divisors (28055202).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21820638 is a wasteful number, since it uses less digits than its factorization.

21820638 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 519551.

The product of its (nonzero) digits is 4608, while the sum is 30.

The square root of 21820638 is about 4671.2565761260. The cubic root of 21820638 is about 279.4403703212.

The spelling of 21820638 in words is "twenty-one million, eight hundred twenty thousand, six hundred thirty-eight".