20991983 has 4 divisors (see below), whose sum is σ = 21184680. Its totient is φ = 20799288.

The previous prime is 20991977. The next prime is 20991989. The reversal of 20991983 is 38919902.

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

It is an interprime number because it is at equal distance from previous prime (20991977) and next prime (20991989).

It is a cyclic number.

It is not a de Polignac number, because 20991983 - 2⁴ = 20991967 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 20991983.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20991989) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 96185 + ... + 96402.

It is an arithmetic number, because the mean of its divisors is an integer number (5296170).

Almost surely, 2^20991983 is an apocalyptic number.

20991983 is a deficient number, since it is larger than the sum of its proper divisors (192697).

20991983 is a wasteful number, since it uses less digits than its factorization.

20991983 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 192696.

The product of its (nonzero) digits is 34992, while the sum is 41.

The square root of 20991983 is about 4581.7008850426. The cubic root of 20991983 is about 275.8573047645.

The spelling of 20991983 in words is "twenty million, nine hundred ninety-one thousand, nine hundred eighty-three".