21975997 has 4 divisors (see below), whose sum is σ = 22733820. Its totient is φ = 21218176.

The previous prime is 21975949. The next prime is 21976001. The reversal of 21975997 is 79957912.

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 3606201 + 18369796 = 1899^2 + 4286^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21975997 is a prime.

It is a Smith number, since the sum of its digits (49) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21975997.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21972997) 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, 378868 + ... + 378925.

It is an arithmetic number, because the mean of its divisors is an integer number (5683455).

Almost surely, 2^21975997 is an apocalyptic number.

It is an amenable number.

21975997 is a deficient number, since it is larger than the sum of its proper divisors (757823).

21975997 is an equidigital number, since it uses as much as digits as its factorization.

21975997 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 757822.

The product of its digits is 357210, while the sum is 49.

The square root of 21975997 is about 4687.8563331228. The cubic root of 21975997 is about 280.1019909062.

The spelling of 21975997 in words is "twenty-one million, nine hundred seventy-five thousand, nine hundred ninety-seven".