21507109 has 6 divisors (see below), whose sum is σ = 23288946. Its totient is φ = 19852560.

The previous prime is 21507103. The next prime is 21507133. The reversal of 21507109 is 90170512.

It can be written as a sum of positive squares in 3 ways, for example, as 850084 + 20657025 = 922^2 + 4545^2 .

It is not a de Polignac number, because 21507109 - 2⁵ = 21507077 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21507103) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 63462 + ... + 63799.

It is an arithmetic number, because the mean of its divisors is an integer number (3881491).

Almost surely, 2^21507109 is an apocalyptic number.

It is an amenable number.

21507109 is a deficient number, since it is larger than the sum of its proper divisors (1781837).

21507109 is a wasteful number, since it uses less digits than its factorization.

21507109 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 127287 (or 127274 counting only the distinct ones).

The product of its (nonzero) digits is 630, while the sum is 25.

The square root of 21507109 is about 4637.5757675751. The cubic root of 21507109 is about 278.0955324417.

The spelling of 21507109 in words is "twenty-one million, five hundred seven thousand, one hundred nine".