21129405 has 32 divisors (see below), whose sum is σ = 37888128. Its totient is φ = 9964800.

The previous prime is 21129403. The next prime is 21129439. The reversal of 21129405 is 50492112.

It is not a de Polignac number, because 21129405 - 2¹ = 21129403 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21129403) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 4375 + ... + 7835.

It is an arithmetic number, because the mean of its divisors is an integer number (1184004).

Almost surely, 2^21129405 is an apocalyptic number.

It is an amenable number.

21129405 is a deficient number, since it is larger than the sum of its proper divisors (16758723).

21129405 is a wasteful number, since it uses less digits than its factorization.

21129405 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3517.

The product of its (nonzero) digits is 720, while the sum is 24.

The square root of 21129405 is about 4596.6732535607. The cubic root of 21129405 is about 276.4579537494.

The spelling of 21129405 in words is "twenty-one million, one hundred twenty-nine thousand, four hundred five".