20991535 has 4 divisors (see below), whose sum is σ = 25189848. Its totient is φ = 16793224.

The previous prime is 20991533. The next prime is 20991577. The reversal of 20991535 is 53519902.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 20991535 - 2¹ = 20991533 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 20991535.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20991533) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2099149 + ... + 2099158.

It is an arithmetic number, because the mean of its divisors is an integer number (6297462).

Almost surely, 2^20991535 is an apocalyptic number.

20991535 is a deficient number, since it is larger than the sum of its proper divisors (4198313).

20991535 is an equidigital number, since it uses as much as digits as its factorization.

20991535 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4198312.

The product of its (nonzero) digits is 12150, while the sum is 34.

The square root of 20991535 is about 4581.6519946412. The cubic root of 20991535 is about 275.8553423494.

The spelling of 20991535 in words is "twenty million, nine hundred ninety-one thousand, five hundred thirty-five".