21643955 has 8 divisors (see below), whose sum is σ = 26133072. Its totient is φ = 17208288.

The previous prime is 21643939. The next prime is 21643961. The reversal of 21643955 is 55934612.

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 21643955 - 2⁴ = 21643939 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 (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 12464 + ... + 14093.

It is an arithmetic number, because the mean of its divisors is an integer number (3266634).

Almost surely, 2^21643955 is an apocalyptic number.

21643955 is a deficient number, since it is larger than the sum of its proper divisors (4489117).

21643955 is a wasteful number, since it uses less digits than its factorization.

21643955 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26725.

The product of its digits is 32400, while the sum is 35.

The square root of 21643955 is about 4652.3064172516. The cubic root of 21643955 is about 278.6841103893.

The spelling of 21643955 in words is "twenty-one million, six hundred forty-three thousand, nine hundred fifty-five".