20991523 has 8 divisors (see below), whose sum is σ = 25253120. Its totient is φ = 17045640.

The previous prime is 20991521. The next prime is 20991527. The reversal of 20991523 is 32519902.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 20991523 - 2¹ = 20991521 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20991521) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 78783 + ... + 79048.

It is an arithmetic number, because the mean of its divisors is an integer number (3156640).

Almost surely, 2^20991523 is an apocalyptic number.

20991523 is a deficient number, since it is larger than the sum of its proper divisors (4261597).

20991523 is a wasteful number, since it uses less digits than its factorization.

20991523 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 157857.

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

The square root of 20991523 is about 4581.6506850697. The cubic root of 20991523 is about 275.8552897844.

The spelling of 20991523 in words is "twenty million, nine hundred ninety-one thousand, five hundred twenty-three".