21640615 has 4 divisors (see below), whose sum is σ = 25968744. Its totient is φ = 17312488.

The previous prime is 21640613. The next prime is 21640621. The reversal of 21640615 is 51604612.

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 21640615 - 2¹ = 21640613 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 21640615.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21640613) 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, 2164057 + ... + 2164066.

It is an arithmetic number, because the mean of its divisors is an integer number (6492186).

Almost surely, 2^21640615 is an apocalyptic number.

21640615 is a deficient number, since it is larger than the sum of its proper divisors (4328129).

21640615 is an equidigital number, since it uses as much as digits as its factorization.

21640615 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4328128.

The product of its (nonzero) digits is 1440, while the sum is 25.

The square root of 21640615 is about 4651.9474416635. The cubic root of 21640615 is about 278.6697745495.

The spelling of 21640615 in words is "twenty-one million, six hundred forty thousand, six hundred fifteen".