21930821 has 4 divisors (see below), whose sum is σ = 23924544. Its totient is φ = 19937100.

The previous prime is 21930809. The next prime is 21930851. The reversal of 21930821 is 12803912.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21930821 - 2²² = 17736517 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21930851) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 996845 + ... + 996866.

It is an arithmetic number, because the mean of its divisors is an integer number (5981136).

Almost surely, 2^21930821 is an apocalyptic number.

It is an amenable number.

21930821 is a deficient number, since it is larger than the sum of its proper divisors (1993723).

21930821 is a wasteful number, since it uses less digits than its factorization.

21930821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1993722.

The product of its (nonzero) digits is 864, while the sum is 26.

The square root of 21930821 is about 4683.0354472286. The cubic root of 21930821 is about 279.9099242571.

The spelling of 21930821 in words is "twenty-one million, nine hundred thirty thousand, eight hundred twenty-one".