20921997 has 4 divisors (see below), whose sum is σ = 27896000. Its totient is φ = 13947996.

The previous prime is 20921987. The next prime is 20922017. The reversal of 20921997 is 79912902.

It is a happy number.

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 20921997 - 2⁴ = 20921981 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20921947) 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, 3486997 + ... + 3487002.

It is an arithmetic number, because the mean of its divisors is an integer number (6974000).

Almost surely, 2^20921997 is an apocalyptic number.

It is an amenable number.

20921997 is a deficient number, since it is larger than the sum of its proper divisors (6974003).

20921997 is an equidigital number, since it uses as much as digits as its factorization.

20921997 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6974002.

The product of its (nonzero) digits is 20412, while the sum is 39.

The square root of 20921997 is about 4574.0569519847. The cubic root of 20921997 is about 275.5503995945.

The spelling of 20921997 in words is "twenty million, nine hundred twenty-one thousand, nine hundred ninety-seven".