20997751 has 4 divisors (see below), whose sum is σ = 21072232. Its totient is φ = 20923272.

The previous prime is 20997731. The next prime is 20997761. The reversal of 20997751 is 15779902.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 20997751 - 2⁵ = 20997719 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 (20997701) 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, 36816 + ... + 37381.

It is an arithmetic number, because the mean of its divisors is an integer number (5268058).

Almost surely, 2^20997751 is an apocalyptic number.

20997751 is a deficient number, since it is larger than the sum of its proper divisors (74481).

20997751 is an equidigital number, since it uses as much as digits as its factorization.

20997751 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 74480.

The product of its (nonzero) digits is 39690, while the sum is 40.

The square root of 20997751 is about 4582.3303023680. The cubic root of 20997751 is about 275.8825683651.

The spelling of 20997751 in words is "twenty million, nine hundred ninety-seven thousand, seven hundred fifty-one".