21205312 has 14 divisors (see below), whose sum is σ = 42079418. Its totient is φ = 10602624.

The previous prime is 21205297. The next prime is 21205313. The reversal of 21205312 is 21350212.

It can be written as a sum of positive squares in only one way, i.e., 13719616 + 7485696 = 3704^2 + 2736^2 .

It is a Harshad number since it is a multiple of its sum of digits (16).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21205313) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 165603 + ... + 165730.

Almost surely, 2^21205312 is an apocalyptic number.

It is an amenable number.

21205312 is a deficient number, since it is larger than the sum of its proper divisors (20874106).

21205312 is an equidigital number, since it uses as much as digits as its factorization.

21205312 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 331345 (or 331335 counting only the distinct ones).

The product of its (nonzero) digits is 120, while the sum is 16.

The square root of 21205312 is about 4604.9225834969. The cubic root of 21205312 is about 276.7886148101.

Adding to 21205312 its reverse (21350212), we get a palindrome (42555524).

The spelling of 21205312 in words is "twenty-one million, two hundred five thousand, three hundred twelve".