21308491 has 8 divisors (see below), whose sum is σ = 21785760. Its totient is φ = 20834112.

The previous prime is 21308477. The next prime is 21308509. The reversal of 21308491 is 19480312.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 21308491 - 2²³ = 12919883 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21308431) 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, 21186 + ... + 22168.

It is an arithmetic number, because the mean of its divisors is an integer number (2723220).

Almost surely, 2^21308491 is an apocalyptic number.

21308491 is a deficient number, since it is larger than the sum of its proper divisors (477269).

21308491 is an equidigital number, since it uses as much as digits as its factorization.

21308491 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1445.

The product of its (nonzero) digits is 1728, while the sum is 28.

The square root of 21308491 is about 4616.1121086906. The cubic root of 21308491 is about 277.2368134765.

The spelling of 21308491 in words is "twenty-one million, three hundred eight thousand, four hundred ninety-one".