21945391 has 8 divisors (see below), whose sum is σ = 23844240. Its totient is φ = 20076672.

The previous prime is 21945389. The next prime is 21945397. The reversal of 21945391 is 19354912.

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

It is a cyclic number.

It is not a de Polignac number, because 21945391 - 2¹ = 21945389 is a prime.

It is a super-2 number, since 2×21945391² = 963200372285762, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21945397) 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, 6001 + ... + 8938.

It is an arithmetic number, because the mean of its divisors is an integer number (2980530).

Almost surely, 2^21945391 is an apocalyptic number.

21945391 is a deficient number, since it is larger than the sum of its proper divisors (1898849).

21945391 is a wasteful number, since it uses less digits than its factorization.

21945391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15065.

The product of its digits is 9720, while the sum is 34.

The square root of 21945391 is about 4684.5908039017. The cubic root of 21945391 is about 279.9718976898.

The spelling of 21945391 in words is "twenty-one million, nine hundred forty-five thousand, three hundred ninety-one".