21621399 has 8 divisors (see below), whose sum is σ = 30524400. Its totient is φ = 13566336.

The previous prime is 21621377. The next prime is 21621401. The reversal of 21621399 is 99312612.

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

It is not a de Polignac number, because 21621399 - 2⁸ = 21621143 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21621329) 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, 211924 + ... + 212025.

It is an arithmetic number, because the mean of its divisors is an integer number (3815550).

Almost surely, 2^21621399 is an apocalyptic number.

21621399 is a deficient number, since it is larger than the sum of its proper divisors (8903001).

21621399 is a wasteful number, since it uses less digits than its factorization.

21621399 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 423969.

The product of its digits is 5832, while the sum is 33.

The square root of 21621399 is about 4649.8816113961. The cubic root of 21621399 is about 278.5872675882.

The spelling of 21621399 in words is "twenty-one million, six hundred twenty-one thousand, three hundred ninety-nine".