20991473 has 4 divisors (see below), whose sum is σ = 21101568. Its totient is φ = 20881380.

The previous prime is 20991463. The next prime is 20991493. The reversal of 20991473 is 37419902.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 20991473 - 2⁴ = 20991457 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20991403) 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, 54761 + ... + 55142.

It is an arithmetic number, because the mean of its divisors is an integer number (5275392).

Almost surely, 2^20991473 is an apocalyptic number.

It is an amenable number.

20991473 is a deficient number, since it is larger than the sum of its proper divisors (110095).

20991473 is a wasteful number, since it uses less digits than its factorization.

20991473 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 110094.

The product of its (nonzero) digits is 13608, while the sum is 35.

The square root of 20991473 is about 4581.6452285178. The cubic root of 20991473 is about 275.8550707630.

The spelling of 20991473 in words is "twenty million, nine hundred ninety-one thousand, four hundred seventy-three".