21206440 has 32 divisors (see below), whose sum is σ = 48044160. Its totient is φ = 8424000.

The previous prime is 21206407. The next prime is 21206441. The reversal of 21206440 is 4460212.

It is not an unprimeable number, because it can be changed into a prime (21206441) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4285 + ... + 7795.

It is an arithmetic number, because the mean of its divisors is an integer number (1501380).

Almost surely, 2^21206440 is an apocalyptic number.

21206440 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21206440 is an abundant number, since it is smaller than the sum of its proper divisors (26837720).

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

21206440 is a wasteful number, since it uses less digits than its factorization.

21206440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3673 (or 3669 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 19.

The square root of 21206440 is about 4605.0450594972. The cubic root of 21206440 is about 276.7935225744.

Adding to 21206440 its reverse (4460212), we get a palindrome (25666652).

The spelling of 21206440 in words is "twenty-one million, two hundred six thousand, four hundred forty".