21205040 has 40 divisors (see below), whose sum is σ = 49990848. Its totient is φ = 8363520.

The previous prime is 21205039. The next prime is 21205043. The reversal of 21205040 is 4050212.

It is a tau number, because it is divible by the number of its divisors (40).

It is not an unprimeable number, because it can be changed into a prime (21205043) 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, 4025 + ... + 7655.

Almost surely, 2^21205040 is an apocalyptic number.

21205040 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21205040, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24995424).

21205040 is an abundant number, since it is smaller than the sum of its proper divisors (28785808).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21205040 is a wasteful number, since it uses less digits than its factorization.

21205040 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3717 (or 3711 counting only the distinct ones).

The product of its (nonzero) digits is 80, while the sum is 14.

The square root of 21205040 is about 4604.8930497895. The cubic root of 21205040 is about 276.7874313515.

Adding to 21205040 its reverse (4050212), we get a palindrome (25255252).

The spelling of 21205040 in words is "twenty-one million, two hundred five thousand, forty".