21097709 has 4 divisors (see below), whose sum is σ = 21116316. Its totient is φ = 21079104.

The previous prime is 21097667. The next prime is 21097723. The reversal of 21097709 is 90779012.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 2418025 + 18679684 = 1555^2 + 4322^2 .

It is a cyclic number.

It is not a de Polignac number, because 21097709 - 2¹² = 21093613 is a prime.

It is a super-2 number, since 2×21097709² = 890226650097362, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21097759) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 7484 + ... + 9909.

It is an arithmetic number, because the mean of its divisors is an integer number (5279079).

Almost surely, 2^21097709 is an apocalyptic number.

It is an amenable number.

21097709 is a deficient number, since it is larger than the sum of its proper divisors (18607).

21097709 is a wasteful number, since it uses less digits than its factorization.

21097709 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18606.

The product of its (nonzero) digits is 7938, while the sum is 35.

The square root of 21097709 is about 4593.2242488257. The cubic root of 21097709 is about 276.3196473383.

The spelling of 21097709 in words is "twenty-one million, ninety-seven thousand, seven hundred nine".