21705397 has 8 divisors (see below), whose sum is σ = 24838016. Its totient is φ = 18580752.

The previous prime is 21705389. The next prime is 21705401. The reversal of 21705397 is 79350712.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21705397 - 2³ = 21705389 is a prime.

It is a super-2 number, since 2×21705397² = 942248517855218, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21705317) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5983 + ... + 8899.

It is an arithmetic number, because the mean of its divisors is an integer number (3104752).

Almost surely, 2^21705397 is an apocalyptic number.

It is an amenable number.

21705397 is a deficient number, since it is larger than the sum of its proper divisors (3132619).

21705397 is a wasteful number, since it uses less digits than its factorization.

21705397 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3987.

The product of its (nonzero) digits is 13230, while the sum is 34.

The square root of 21705397 is about 4658.9051288903. The cubic root of 21705397 is about 278.9475670450.

The spelling of 21705397 in words is "twenty-one million, seven hundred five thousand, three hundred ninety-seven".