21907820 has 24 divisors (see below), whose sum is σ = 50189328. Its totient is φ = 7966400.

The previous prime is 21907813. The next prime is 21907829. The reversal of 21907820 is 2870912.

It is a happy number.

It is not an unprimeable number, because it can be changed into a prime (21907829) 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, 49571 + ... + 50010.

It is an arithmetic number, because the mean of its divisors is an integer number (2091222).

Almost surely, 2^21907820 is an apocalyptic number.

21907820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21907820 is an abundant number, since it is smaller than the sum of its proper divisors (28281508).

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

21907820 is a wasteful number, since it uses less digits than its factorization.

21907820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 99601 (or 99599 counting only the distinct ones).

The product of its (nonzero) digits is 2016, while the sum is 29.

The square root of 21907820 is about 4680.5790240097. The cubic root of 21907820 is about 279.8120337089.

The spelling of 21907820 in words is "twenty-one million, nine hundred seven thousand, eight hundred twenty".