21240909 has 6 divisors (see below), whose sum is σ = 30681326. Its totient is φ = 14160600.

The previous prime is 21240907. The next prime is 21240913. The reversal of 21240909 is 90904212.

It can be written as a sum of positive squares in only one way, i.e., 18275625 + 2965284 = 4275^2 + 1722^2 .

It is not a de Polignac number, because 21240909 - 2¹ = 21240907 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 (21240907) 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, 1180042 + ... + 1180059.

Almost surely, 2^21240909 is an apocalyptic number.

It is an amenable number.

21240909 is a deficient number, since it is larger than the sum of its proper divisors (9440417).

21240909 is a wasteful number, since it uses less digits than its factorization.

21240909 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2360107 (or 2360104 counting only the distinct ones).

The product of its (nonzero) digits is 1296, while the sum is 27.

The square root of 21240909 is about 4608.7860657661. The cubic root of 21240909 is about 276.9434083541.

The spelling of 21240909 in words is "twenty-one million, two hundred forty thousand, nine hundred nine".