20997640 has 16 divisors (see below), whose sum is σ = 47244780. Its totient is φ = 8399040.

The previous prime is 20997637. The next prime is 20997649. The reversal of 20997640 is 4679902.

It can be written as a sum of positive squares in 2 ways, for example, as 20994724 + 2916 = 4582^2 + 54^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 20997640.

It is not an unprimeable number, because it can be changed into a prime (20997649) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 262431 + ... + 262510.

Almost surely, 2^20997640 is an apocalyptic number.

20997640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

20997640 is an abundant number, since it is smaller than the sum of its proper divisors (26247140).

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

20997640 is a wasteful number, since it uses less digits than its factorization.

20997640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 524952 (or 524948 counting only the distinct ones).

The product of its (nonzero) digits is 27216, while the sum is 37.

The square root of 20997640 is about 4582.3181906105. The cubic root of 20997640 is about 275.8820822334.

The spelling of 20997640 in words is "twenty million, nine hundred ninety-seven thousand, six hundred forty".