21945901 has 4 divisors (see below), whose sum is σ = 22159072. Its totient is φ = 21732732.

The previous prime is 21945881. The next prime is 21945907. The reversal of 21945901 is 10954912.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21945901 - 2⁹ = 21945389 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 (21945907) 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, 106431 + ... + 106636.

It is an arithmetic number, because the mean of its divisors is an integer number (5539768).

Almost surely, 2^21945901 is an apocalyptic number.

It is an amenable number.

21945901 is a deficient number, since it is larger than the sum of its proper divisors (213171).

21945901 is a wasteful number, since it uses less digits than its factorization.

21945901 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 213170.

The product of its (nonzero) digits is 3240, while the sum is 31.

The square root of 21945901 is about 4684.6452373686. The cubic root of 21945901 is about 279.9740664757.

The spelling of 21945901 in words is "twenty-one million, nine hundred forty-five thousand, nine hundred one".