21906621 has 24 divisors (see below), whose sum is σ = 34968960. Its totient is φ = 13104000.

The previous prime is 21906617. The next prime is 21906631. The reversal of 21906621 is 12660912.

It is not a de Polignac number, because 21906621 - 2² = 21906617 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21906631) 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 23 ways as a sum of consecutive naturals, for example, 6421 + ... + 9221.

It is an arithmetic number, because the mean of its divisors is an integer number (1457040).

Almost surely, 2^21906621 is an apocalyptic number.

It is an amenable number.

21906621 is a deficient number, since it is larger than the sum of its proper divisors (13062339).

21906621 is a wasteful number, since it uses less digits than its factorization.

21906621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2897 (or 2894 counting only the distinct ones).

The product of its (nonzero) digits is 1296, while the sum is 27.

The square root of 21906621 is about 4680.4509398134. The cubic root of 21906621 is about 279.8069289754.

The spelling of 21906621 in words is "twenty-one million, nine hundred six thousand, six hundred twenty-one".