21215909 has 16 divisors (see below), whose sum is σ = 25220160. Its totient is φ = 17592960.

The previous prime is 21215893. The next prime is 21215921. The reversal of 21215909 is 90951212.

It is not a de Polignac number, because 21215909 - 2⁴ = 21215893 is a prime.

It is a super-2 number, since 2×21215909² = 900229589392562, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21215939) 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, 11894 + ... + 13560.

It is an arithmetic number, because the mean of its divisors is an integer number (1576260).

Almost surely, 2^21215909 is an apocalyptic number.

It is an amenable number.

21215909 is a deficient number, since it is larger than the sum of its proper divisors (4004251).

21215909 is a wasteful number, since it uses less digits than its factorization.

21215909 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1780.

The product of its (nonzero) digits is 1620, while the sum is 29.

The square root of 21215909 is about 4606.0730563030. The cubic root of 21215909 is about 276.8347139588.

The spelling of 21215909 in words is "twenty-one million, two hundred fifteen thousand, nine hundred nine".