21191905 has 16 divisors (see below), whose sum is σ = 29741184. Its totient is φ = 14192640.

The previous prime is 21191873. The next prime is 21191917. The reversal of 21191905 is 50919112.

It is not a de Polignac number, because 21191905 - 2⁵ = 21191873 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 5536 + ... + 8545.

It is an arithmetic number, because the mean of its divisors is an integer number (1858824).

Almost surely, 2^21191905 is an apocalyptic number.

It is an amenable number.

21191905 is a deficient number, since it is larger than the sum of its proper divisors (8549279).

21191905 is a wasteful number, since it uses less digits than its factorization.

21191905 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14136.

The product of its (nonzero) digits is 810, while the sum is 28.

The square root of 21191905 is about 4603.4666285312. The cubic root of 21191905 is about 276.7302695662.

The spelling of 21191905 in words is "twenty-one million, one hundred ninety-one thousand, nine hundred five".