21891905 has 8 divisors (see below), whose sum is σ = 30023232. Its totient is φ = 15011568.

The previous prime is 21891889. The next prime is 21891907. The reversal of 21891905 is 50919812.

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 21891905 - 2⁴ = 21891889 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (35), and also a Moran number because the ratio is a prime number: 625483 = 21891905 / (2 + 1 + 8 + 9 + 1 + 9 + 0 + 5).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21891907) 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, 312707 + ... + 312776.

It is an arithmetic number, because the mean of its divisors is an integer number (3752904).

Almost surely, 2^21891905 is an apocalyptic number.

It is an amenable number.

21891905 is a deficient number, since it is larger than the sum of its proper divisors (8131327).

21891905 is an equidigital number, since it uses as much as digits as its factorization.

21891905 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 625495.

The product of its (nonzero) digits is 6480, while the sum is 35.

The square root of 21891905 is about 4678.8786049651. The cubic root of 21891905 is about 279.7442605378.

The spelling of 21891905 in words is "twenty-one million, eight hundred ninety-one thousand, nine hundred five".