20521399 has 2 divisors, whose sum is σ = 20521400. Its totient is φ = 20521398.

The previous prime is 20521393. The next prime is 20521409. The reversal of 20521399 is 99312502.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 20521399 - 2⁷ = 20521271 is a prime.

It is a super-2 number, since 2×20521399² = 842255633834402, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 20521399.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20521393) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10260699 + 10260700.

It is an arithmetic number, because the mean of its divisors is an integer number (10260700).

Almost surely, 2^20521399 is an apocalyptic number.

20521399 is a deficient number, since it is larger than the sum of its proper divisors (1).

20521399 is an equidigital number, since it uses as much as digits as its factorization.

20521399 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 4860, while the sum is 31.

The square root of 20521399 is about 4530.0550769279. The cubic root of 20521399 is about 273.7803797175.

The spelling of 20521399 in words is "twenty million, five hundred twenty-one thousand, three hundred ninety-nine".