21640643 has 8 divisors (see below), whose sum is σ = 23129712. Its totient is φ = 20175616.

The previous prime is 21640637. The next prime is 21640651. The reversal of 21640643 is 34604612.

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 21640643 - 2²² = 17446339 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21640613) 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, 4130 + ... + 7767.

It is an arithmetic number, because the mean of its divisors is an integer number (2891214).

Almost surely, 2^21640643 is an apocalyptic number.

21640643 is a deficient number, since it is larger than the sum of its proper divisors (1489069).

21640643 is a wasteful number, since it uses less digits than its factorization.

21640643 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12021.

The product of its (nonzero) digits is 3456, while the sum is 26.

The square root of 21640643 is about 4651.9504511549. The cubic root of 21640643 is about 278.6698947363.

The spelling of 21640643 in words is "twenty-one million, six hundred forty thousand, six hundred forty-three".