21536729 has 4 divisors (see below), whose sum is σ = 21546240. Its totient is φ = 21527220.

The previous prime is 21536707. The next prime is 21536737. The reversal of 21536729 is 92763512.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21536729 - 2¹² = 21532633 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21536759) 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, 824 + ... + 6614.

It is an arithmetic number, because the mean of its divisors is an integer number (5386560).

Almost surely, 2^21536729 is an apocalyptic number.

It is an amenable number.

21536729 is a deficient number, since it is larger than the sum of its proper divisors (9511).

21536729 is an equidigital number, since it uses as much as digits as its factorization.

21536729 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9510.

The product of its digits is 22680, while the sum is 35.

The square root of 21536729 is about 4640.7681476238. The cubic root of 21536729 is about 278.2231400324.

The spelling of 21536729 in words is "twenty-one million, five hundred thirty-six thousand, seven hundred twenty-nine".