20997 has 6 divisors (see below), whose sum is σ = 30342. Its totient is φ = 13992.

The previous prime is 20983. The next prime is 21001. The reversal of 20997 is 79902.

It can be written as a sum of positive squares in only one way, i.e., 16641 + 4356 = 129^2 + 66^2 .

It is not a de Polignac number, because 20997 - 2⁴ = 20981 is a prime.

It is a nialpdrome in base 13.

It is a self number, because there is not a number n which added to its sum of digits gives 20997.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20947) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1158 + ... + 1175.

It is an arithmetic number, because the mean of its divisors is an integer number (5057).

2²⁰⁹⁹⁷ is an apocalyptic number.

It is an amenable number.

20997 is a deficient number, since it is larger than the sum of its proper divisors (9345).

20997 is a wasteful number, since it uses less digits than its factorization.

20997 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2339 (or 2336 counting only the distinct ones).

The product of its (nonzero) digits is 1134, while the sum is 27.

The square root of 20997 is about 144.9034161088. The cubic root of 20997 is about 27.5879279278.

The spelling of 20997 in words is "twenty thousand, nine hundred ninety-seven".