21213660 has 48 divisors (see below), whose sum is σ = 63969696. Its totient is φ = 5221632.

The previous prime is 21213631. The next prime is 21213667. The reversal of 21213660 is 6631212.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21213667) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 12819 + ... + 14378.

It is an arithmetic number, because the mean of its divisors is an integer number (1332702).

Almost surely, 2^21213660 is an apocalyptic number.

21213660 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21213660 is an abundant number, since it is smaller than the sum of its proper divisors (42756036).

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

21213660 is a wasteful number, since it uses less digits than its factorization.

21213660 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27222 (or 27220 counting only the distinct ones).

The product of its (nonzero) digits is 432, while the sum is 21.

The square root of 21213660 is about 4605.8289156242. The cubic root of 21213660 is about 276.8249316256.

Adding to 21213660 its reverse (6631212), we get a palindrome (27844872).

The spelling of 21213660 in words is "twenty-one million, two hundred thirteen thousand, six hundred sixty".