21207491 has 4 divisors (see below), whose sum is σ = 21567000. Its totient is φ = 20847984.

The previous prime is 21207469. The next prime is 21207493. The reversal of 21207491 is 19470212.

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 21207491 - 2²² = 17013187 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21207491.

It is not an unprimeable number, because it can be changed into a prime (21207493) 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, 179666 + ... + 179783.

It is an arithmetic number, because the mean of its divisors is an integer number (5391750).

Almost surely, 2^21207491 is an apocalyptic number.

21207491 is a deficient number, since it is larger than the sum of its proper divisors (359509).

21207491 is an equidigital number, since it uses as much as digits as its factorization.

21207491 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 359508.

The product of its (nonzero) digits is 1008, while the sum is 26.

The square root of 21207491 is about 4605.1591720591. The cubic root of 21207491 is about 276.7980951663.

The spelling of 21207491 in words is "twenty-one million, two hundred seven thousand, four hundred ninety-one".