21997745 has 32 divisors (see below), whose sum is σ = 34857216. Its totient is φ = 12902400.

The previous prime is 21997733. The next prime is 21997751. The reversal of 21997745 is 54779912.

It is not a de Polignac number, because 21997745 - 2⁶ = 21997681 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21997696 and 21997705.

It is an unprimeable number.

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 31 ways as a sum of consecutive naturals, for example, 4865 + ... + 8225.

It is an arithmetic number, because the mean of its divisors is an integer number (1089288).

Almost surely, 2^21997745 is an apocalyptic number.

It is an amenable number.

21997745 is a deficient number, since it is larger than the sum of its proper divisors (12859471).

21997745 is a wasteful number, since it uses less digits than its factorization.

21997745 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3401.

The product of its digits is 158760, while the sum is 44.

The square root of 21997745 is about 4690.1753698556. The cubic root of 21997745 is about 280.1943591040.

It can be divided in two parts, 219977 and 45, that added together give a palindrome (220022).

The spelling of 21997745 in words is "twenty-one million, nine hundred ninety-seven thousand, seven hundred forty-five".