21405729 has 8 divisors (see below), whose sum is σ = 28645120. Its totient is φ = 14218416.

The previous prime is 21405691. The next prime is 21405733. The reversal of 21405729 is 92750412.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21405729 - 2⁸ = 21405473 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21405696 and 21405705.

It is not an unprimeable number, because it can be changed into a prime (21405749) 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, 12049 + ... + 13710.

It is an arithmetic number, because the mean of its divisors is an integer number (3580640).

Almost surely, 2^21405729 is an apocalyptic number.

It is an amenable number.

21405729 is a deficient number, since it is larger than the sum of its proper divisors (7239391).

21405729 is a wasteful number, since it uses less digits than its factorization.

21405729 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 26039.

The product of its (nonzero) digits is 5040, while the sum is 30.

The square root of 21405729 is about 4626.6325767236. The cubic root of 21405729 is about 277.6578827233.

The spelling of 21405729 in words is "twenty-one million, four hundred five thousand, seven hundred twenty-nine".