21242109 has 16 divisors (see below), whose sum is σ = 32555520. Its totient is φ = 12068400.

The previous prime is 21242101. The next prime is 21242131. The reversal of 21242109 is 90124212.

It is not a de Polignac number, because 21242109 - 2³ = 21242101 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21242101) 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 15 ways as a sum of consecutive naturals, for example, 934 + ... + 6584.

It is an arithmetic number, because the mean of its divisors is an integer number (2034720).

Almost surely, 2^21242109 is an apocalyptic number.

It is an amenable number.

21242109 is a deficient number, since it is larger than the sum of its proper divisors (11313411).

21242109 is a wasteful number, since it uses less digits than its factorization.

21242109 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5840.

The product of its (nonzero) digits is 288, while the sum is 21.

The square root of 21242109 is about 4608.9162500527. The cubic root of 21242109 is about 276.9486235395.

The spelling of 21242109 in words is "twenty-one million, two hundred forty-two thousand, one hundred nine".