20997921 has 24 divisors (see below), whose sum is σ = 32979744. Its totient is φ = 11847360.

The previous prime is 20997917. The next prime is 20997931. The reversal of 20997921 is 12979902.

It is a happy number.

It is not a de Polignac number, because 20997921 - 2² = 20997917 is a prime.

It is a Smith number, since the sum of its digits (39) coincides with the sum of the digits of its prime factors.

It is a self number, because there is not a number n which added to its sum of digits gives 20997921.

It is not an unprimeable number, because it can be changed into a prime (20997901) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 11341 + ... + 13061.

It is an arithmetic number, because the mean of its divisors is an integer number (1374156).

Almost surely, 2^20997921 is an apocalyptic number.

20997921 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

20997921 is a deficient number, since it is larger than the sum of its proper divisors (11981823).

20997921 is a wasteful number, since it uses less digits than its factorization.

20997921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1821 (or 1814 counting only the distinct ones).

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

The square root of 20997921 is about 4582.3488518444. The cubic root of 20997921 is about 275.8833128879.

The spelling of 20997921 in words is "twenty million, nine hundred ninety-seven thousand, nine hundred twenty-one".