21929399 has 4 divisors (see below), whose sum is σ = 21943320. Its totient is φ = 21915480.

The previous prime is 21929393. The next prime is 21929437. The reversal of 21929399 is 99392912.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21929399 - 2¹² = 21925303 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 (21929393) 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, 4244 + ... + 7865.

It is an arithmetic number, because the mean of its divisors is an integer number (5485830).

Almost surely, 2^21929399 is an apocalyptic number.

21929399 is a deficient number, since it is larger than the sum of its proper divisors (13921).

21929399 is a wasteful number, since it uses less digits than its factorization.

21929399 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13920.

The product of its digits is 78732, while the sum is 44.

The square root of 21929399 is about 4682.8836201640. The cubic root of 21929399 is about 279.9038743162.

The spelling of 21929399 in words is "twenty-one million, nine hundred twenty-nine thousand, three hundred ninety-nine".