21729761 has 4 divisors (see below), whose sum is σ = 21783300. Its totient is φ = 21676224.

The previous prime is 21729751. The next prime is 21729781. The reversal of 21729761 is 16792712.

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 19536400 + 2193361 = 4420^2 + 1481^2 .

It is a cyclic number.

It is not a de Polignac number, because 21729761 - 2²² = 17535457 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21729751) 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, 26156 + ... + 26973.

It is an arithmetic number, because the mean of its divisors is an integer number (5445825).

Almost surely, 2^21729761 is an apocalyptic number.

It is an amenable number.

21729761 is a deficient number, since it is larger than the sum of its proper divisors (53539).

21729761 is an equidigital number, since it uses as much as digits as its factorization.

21729761 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 53538.

The product of its digits is 10584, while the sum is 35.

The square root of 21729761 is about 4661.5191729735. The cubic root of 21729761 is about 279.0518995788.

The spelling of 21729761 in words is "twenty-one million, seven hundred twenty-nine thousand, seven hundred sixty-one".