21906643 has 8 divisors (see below), whose sum is σ = 24226416. Its totient is φ = 19641600.

The previous prime is 21906631. The next prime is 21906667. The reversal of 21906643 is 34660912.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21906643 - 2¹⁷ = 21775571 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21906613) 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, 12838 + ... + 14443.

It is an arithmetic number, because the mean of its divisors is an integer number (3028302).

Almost surely, 2^21906643 is an apocalyptic number.

21906643 is a deficient number, since it is larger than the sum of its proper divisors (2319773).

21906643 is a wasteful number, since it uses less digits than its factorization.

21906643 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 27365.

The product of its (nonzero) digits is 7776, while the sum is 31.

The square root of 21906643 is about 4680.4532900137. The cubic root of 21906643 is about 279.8070226419.

The spelling of 21906643 in words is "twenty-one million, nine hundred six thousand, six hundred forty-three".