21401729 has 4 divisors (see below), whose sum is σ = 21558084. Its totient is φ = 21245376.

The previous prime is 21401717. The next prime is 21401761. The reversal of 21401729 is 92710412.

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

It can be written as a sum of positive squares in 2 ways, for example, as 7711729 + 13690000 = 2777^2 + 3700^2 .

It is a cyclic number.

It is not a de Polignac number, because 21401729 - 2⁸ = 21401473 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21401698 and 21401707.

It is not an unprimeable number, because it can be changed into a prime (21404729) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 77972 + ... + 78245.

It is an arithmetic number, because the mean of its divisors is an integer number (5389521).

Almost surely, 2^21401729 is an apocalyptic number.

It is an amenable number.

21401729 is a deficient number, since it is larger than the sum of its proper divisors (156355).

21401729 is a wasteful number, since it uses less digits than its factorization.

21401729 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 156354.

The product of its (nonzero) digits is 1008, while the sum is 26.

The square root of 21401729 is about 4626.2002766850. The cubic root of 21401729 is about 277.6405867193.

The spelling of 21401729 in words is "twenty-one million, four hundred one thousand, seven hundred twenty-nine".