21597973 has 8 divisors (see below), whose sum is σ = 23487192. Its totient is φ = 19777536.

The previous prime is 21597971. The next prime is 21598013. The reversal of 21597973 is 37979512.

It can be written as a sum of positive squares in 4 ways, for example, as 9778129 + 11819844 = 3127^2 + 3438^2 .

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

It is not a de Polignac number, because 21597973 - 2¹ = 21597971 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 (21597971) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 16540 + ... + 17797.

It is an arithmetic number, because the mean of its divisors is an integer number (2935899).

Almost surely, 2^21597973 is an apocalyptic number.

It is an amenable number.

21597973 is a deficient number, since it is larger than the sum of its proper divisors (1889219).

21597973 is a wasteful number, since it uses less digits than its factorization.

21597973 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 34391.

The product of its digits is 119070, while the sum is 43.

The square root of 21597973 is about 4647.3619398536. The cubic root of 21597973 is about 278.4866181696.

The spelling of 21597973 in words is "twenty-one million, five hundred ninety-seven thousand, nine hundred seventy-three".