21231491 has 4 divisors (see below), whose sum is σ = 21281184. Its totient is φ = 21181800.

The previous prime is 21231473. The next prime is 21231499. The reversal of 21231491 is 19413212.

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 21231491 - 2¹⁴ = 21215107 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21231499) 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, 24200 + ... + 25061.

It is an arithmetic number, because the mean of its divisors is an integer number (5320296).

Almost surely, 2^21231491 is an apocalyptic number.

21231491 is a deficient number, since it is larger than the sum of its proper divisors (49693).

21231491 is an equidigital number, since it uses as much as digits as its factorization.

21231491 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 49692.

The product of its digits is 432, while the sum is 23.

The square root of 21231491 is about 4607.7642083770. The cubic root of 21231491 is about 276.9024710194.

The spelling of 21231491 in words is "twenty-one million, two hundred thirty-one thousand, four hundred ninety-one".