21640435 has 4 divisors (see below), whose sum is σ = 25968528. Its totient is φ = 17312344.

The previous prime is 21640427. The next prime is 21640441. The reversal of 21640435 is 53404612.

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 21640435 - 2³ = 21640427 is a prime.

It is a Duffinian number.

It is an unprimeable number.

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, 2164039 + ... + 2164048.

It is an arithmetic number, because the mean of its divisors is an integer number (6492132).

Almost surely, 2^21640435 is an apocalyptic number.

21640435 is a deficient number, since it is larger than the sum of its proper divisors (4328093).

21640435 is an equidigital number, since it uses as much as digits as its factorization.

21640435 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4328092.

The product of its (nonzero) digits is 2880, while the sum is 25.

The square root of 21640435 is about 4651.9280948871. The cubic root of 21640435 is about 278.6690019175.

The spelling of 21640435 in words is "twenty-one million, six hundred forty thousand, four hundred thirty-five".