21191904 has 36 divisors (see below), whose sum is σ = 60265296. Its totient is φ = 7063872.

The previous prime is 21191873. The next prime is 21191917. The reversal of 21191904 is 40919112.

It is a tau number, because it is divible by the number of its divisors (36).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 36504 + ... + 37079.

It is an arithmetic number, because the mean of its divisors is an integer number (1674036).

Almost surely, 2^21191904 is an apocalyptic number.

21191904 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21191904 is an abundant number, since it is smaller than the sum of its proper divisors (39073392).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21191904 is a wasteful number, since it uses less digits than its factorization.

21191904 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 73599 (or 73588 counting only the distinct ones).

The product of its (nonzero) digits is 648, while the sum is 27.

The square root of 21191904 is about 4603.4665199174. The cubic root of 21191904 is about 276.7302652134.

The spelling of 21191904 in words is "twenty-one million, one hundred ninety-one thousand, nine hundred four".