21306491 has 4 divisors (see below), whose sum is σ = 22559832. Its totient is φ = 20053152.

The previous prime is 21306479. The next prime is 21306539. The reversal of 21306491 is 19460312.

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 21306491 - 2¹⁸ = 21044347 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 21306491.

It is not an unprimeable number, because it can be changed into a prime (21306431) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 626645 + ... + 626678.

It is an arithmetic number, because the mean of its divisors is an integer number (5639958).

Almost surely, 2^21306491 is an apocalyptic number.

21306491 is a deficient number, since it is larger than the sum of its proper divisors (1253341).

21306491 is a wasteful number, since it uses less digits than its factorization.

21306491 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1253340.

The product of its (nonzero) digits is 1296, while the sum is 26.

The square root of 21306491 is about 4615.8954710868. The cubic root of 21306491 is about 277.2281394543.

The spelling of 21306491 in words is "twenty-one million, three hundred six thousand, four hundred ninety-one".