21371909 has 6 divisors (see below), whose sum is σ = 23142546. Its totient is φ = 19727760.

The previous prime is 21371893. The next prime is 21371929. The reversal of 21371909 is 90917312.

It is a happy number.

It can be written as a sum of positive squares in 3 ways, for example, as 9025 + 21362884 = 95^2 + 4622^2 .

It is not a de Polignac number, because 21371909 - 2⁴ = 21371893 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 (21371929) 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, 63062 + ... + 63399.

It is an arithmetic number, because the mean of its divisors is an integer number (3857091).

Almost surely, 2^21371909 is an apocalyptic number.

It is an amenable number.

21371909 is a deficient number, since it is larger than the sum of its proper divisors (1770637).

21371909 is a wasteful number, since it uses less digits than its factorization.

21371909 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 126487 (or 126474 counting only the distinct ones).

The product of its (nonzero) digits is 3402, while the sum is 32.

The square root of 21371909 is about 4622.9762058657. The cubic root of 21371909 is about 277.5115770405.

The spelling of 21371909 in words is "twenty-one million, three hundred seventy-one thousand, nine hundred nine".