21965921 has 4 divisors (see below), whose sum is σ = 23258052. Its totient is φ = 20673792.

The previous prime is 21965899. The next prime is 21965927. The reversal of 21965921 is 12956912.

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 7639696 + 14326225 = 2764^2 + 3785^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21965921 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21965927) 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, 646040 + ... + 646073.

It is an arithmetic number, because the mean of its divisors is an integer number (5814513).

Almost surely, 2^21965921 is an apocalyptic number.

It is an amenable number.

21965921 is a deficient number, since it is larger than the sum of its proper divisors (1292131).

21965921 is a wasteful number, since it uses less digits than its factorization.

21965921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1292130.

The product of its digits is 9720, while the sum is 35.

The square root of 21965921 is about 4686.7815182703. The cubic root of 21965921 is about 280.0591754181.

Subtracting from 21965921 its reverse (12956912), we obtain a palindrome (9009009).

The spelling of 21965921 in words is "twenty-one million, nine hundred sixty-five thousand, nine hundred twenty-one".