20856191 has 4 divisors (see below), whose sum is σ = 21575400. Its totient is φ = 20136984.

The previous prime is 20856181. The next prime is 20856221. The reversal of 20856191 is 19165802.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19165802 = 2 ⋅9582901.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20856191 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20856131) 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, 359561 + ... + 359618.

It is an arithmetic number, because the mean of its divisors is an integer number (5393850).

Almost surely, 2^20856191 is an apocalyptic number.

20856191 is a deficient number, since it is larger than the sum of its proper divisors (719209).

20856191 is an equidigital number, since it uses as much as digits as its factorization.

20856191 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 719208.

The product of its (nonzero) digits is 4320, while the sum is 32.

The square root of 20856191 is about 4566.8578913735. The cubic root of 20856191 is about 275.2611997633.

The spelling of 20856191 in words is "twenty million, eight hundred fifty-six thousand, one hundred ninety-one".