21405919 has 4 divisors (see below), whose sum is σ = 21676960. Its totient is φ = 21134880.

The previous prime is 21405899. The next prime is 21405931. The reversal of 21405919 is 91950412.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21405919 - 2⁵ = 21405887 is a prime.

It is a super-2 number, since 2×21405919² = 916426736469122, 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 (21405619) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 135402 + ... + 135559.

It is an arithmetic number, because the mean of its divisors is an integer number (5419240).

Almost surely, 2^21405919 is an apocalyptic number.

21405919 is a deficient number, since it is larger than the sum of its proper divisors (271041).

21405919 is an equidigital number, since it uses as much as digits as its factorization.

21405919 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 271040.

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

The square root of 21405919 is about 4626.6531099705. The cubic root of 21405919 is about 277.6587042298.

The spelling of 21405919 in words is "twenty-one million, four hundred five thousand, nine hundred nineteen".