21097491 has 4 divisors (see below), whose sum is σ = 28129992. Its totient is φ = 14064992.

The previous prime is 21097487. The next prime is 21097513. The reversal of 21097491 is 19479012.

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 21097491 - 2² = 21097487 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21097421) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3516246 + ... + 3516251.

It is an arithmetic number, because the mean of its divisors is an integer number (7032498).

Almost surely, 2^21097491 is an apocalyptic number.

21097491 is a deficient number, since it is larger than the sum of its proper divisors (7032501).

21097491 is an equidigital number, since it uses as much as digits as its factorization.

21097491 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7032500.

The product of its (nonzero) digits is 4536, while the sum is 33.

The square root of 21097491 is about 4593.2005181572. The cubic root of 21097491 is about 276.3186956095.

The spelling of 21097491 in words is "twenty-one million, ninety-seven thousand, four hundred ninety-one".