21205424 has 20 divisors (see below), whose sum is σ = 41157336. Its totient is φ = 10584192.

The previous prime is 21205399. The next prime is 21205447. The reversal of 21205424 is 42450212.

It is a happy number.

It is a junction number, because it is equal to n+sod(n) for n = 21205396 and 21205405.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 15887 + ... + 17169.

Almost surely, 2^21205424 is an apocalyptic number.

It is an amenable number.

21205424 is a deficient number, since it is larger than the sum of its proper divisors (19951912).

21205424 is a wasteful number, since it uses less digits than its factorization.

21205424 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2324 (or 2318 counting only the distinct ones).

The product of its (nonzero) digits is 640, while the sum is 20.

The square root of 21205424 is about 4604.9347443802. The cubic root of 21205424 is about 276.7891021136.

Adding to 21205424 its reverse (42450212), we get a palindrome (63655636).

It can be divided in two parts, 21205 and 424, that multiplied together give a triangular number (8990920 = T₄₂₄₀).

The spelling of 21205424 in words is "twenty-one million, two hundred five thousand, four hundred twenty-four".