21947109 has 16 divisors (see below), whose sum is σ = 31180800. Its totient is φ = 13691376.

The previous prime is 21947099. The next prime is 21947111. The reversal of 21947109 is 90174912.

It is not a de Polignac number, because 21947109 - 2⁵ = 21947077 is a prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21947109.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21947309) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2412 + ... + 7050.

It is an arithmetic number, because the mean of its divisors is an integer number (1948800).

Almost surely, 2^21947109 is an apocalyptic number.

It is an amenable number.

21947109 is a deficient number, since it is larger than the sum of its proper divisors (9233691).

21947109 is a wasteful number, since it uses less digits than its factorization.

21947109 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4744.

The product of its (nonzero) digits is 4536, while the sum is 33.

The square root of 21947109 is about 4684.7741674493. The cubic root of 21947109 is about 279.9792033874.

The spelling of 21947109 in words is "twenty-one million, nine hundred forty-seven thousand, one hundred nine".