20905891 has 4 divisors (see below), whose sum is σ = 21034312. Its totient is φ = 20777472.

The previous prime is 20905877. The next prime is 20905901. The reversal of 20905891 is 19850902.

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

It is a cyclic number.

It is not a de Polignac number, because 20905891 - 2²¹ = 18808739 is a prime.

It is a super-3 number, since 3×20905891³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20905831) 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, 63966 + ... + 64291.

It is an arithmetic number, because the mean of its divisors is an integer number (5258578).

Almost surely, 2^20905891 is an apocalyptic number.

20905891 is a deficient number, since it is larger than the sum of its proper divisors (128421).

20905891 is a wasteful number, since it uses less digits than its factorization.

20905891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 128420.

The product of its (nonzero) digits is 6480, while the sum is 34.

The square root of 20905891 is about 4572.2960315360. The cubic root of 20905891 is about 275.4796741273.

The spelling of 20905891 in words is "twenty million, nine hundred five thousand, eight hundred ninety-one".