20921818 has 16 divisors (see below), whose sum is σ = 32714280. Its totient is φ = 10022656.

The previous prime is 20921809. The next prime is 20921819. The reversal of 20921818 is 81812902.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 15737089 + 5184729 = 3967^2 + 2277^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 20921818.

It is not an unprimeable number, because it can be changed into a prime (20921819) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 6630 + ... + 9262.

Almost surely, 2^20921818 is an apocalyptic number.

20921818 is a deficient number, since it is larger than the sum of its proper divisors (11792462).

20921818 is a wasteful number, since it uses less digits than its factorization.

20921818 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2801.

The product of its (nonzero) digits is 2304, while the sum is 31.

The square root of 20921818 is about 4574.0373850680. The cubic root of 20921818 is about 275.5496137603.

The spelling of 20921818 in words is "twenty million, nine hundred twenty-one thousand, eight hundred eighteen".