21891531 has 8 divisors (see below), whose sum is σ = 29977744. Its totient is φ = 14199840.

The previous prime is 21891511. The next prime is 21891539. The reversal of 21891531 is 13519812.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21891531 - 2¹⁹ = 21367243 is a prime.

It is a super-2 number, since 2×21891531² = 958478259047922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21891539) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 98500 + ... + 98721.

It is an arithmetic number, because the mean of its divisors is an integer number (3747218).

Almost surely, 2^21891531 is an apocalyptic number.

21891531 is a deficient number, since it is larger than the sum of its proper divisors (8086213).

21891531 is a wasteful number, since it uses less digits than its factorization.

21891531 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 197261.

The product of its digits is 2160, while the sum is 30.

The square root of 21891531 is about 4678.8386379528. The cubic root of 21891531 is about 279.7426674839.

It can be divided in two parts, 21891 and 531, that added together give a palindrome (22422).

The spelling of 21891531 in words is "twenty-one million, eight hundred ninety-one thousand, five hundred thirty-one".