20991161 has 4 divisors (see below), whose sum is σ = 21034752. Its totient is φ = 20947572.

The previous prime is 20991149. The next prime is 20991211. The reversal of 20991161 is 16119902.

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 20991161 - 2⁶ = 20991097 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20991101) 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, 21065 + ... + 22038.

It is an arithmetic number, because the mean of its divisors is an integer number (5258688).

Almost surely, 2^20991161 is an apocalyptic number.

It is an amenable number.

20991161 is a deficient number, since it is larger than the sum of its proper divisors (43591).

20991161 is an equidigital number, since it uses as much as digits as its factorization.

20991161 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 43590.

The product of its (nonzero) digits is 972, while the sum is 29.

The square root of 20991161 is about 4581.6111794870. The cubic root of 20991161 is about 275.8537040619.

The spelling of 20991161 in words is "twenty million, nine hundred ninety-one thousand, one hundred sixty-one".