21205739 has 4 divisors (see below), whose sum is σ = 21301056. Its totient is φ = 21110424.

The previous prime is 21205727. The next prime is 21205759. The reversal of 21205739 is 93750212.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21205739 is a prime.

It is a super-2 number, since 2×21205739² = 899366733072242, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21205759) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 47324 + ... + 47769.

It is an arithmetic number, because the mean of its divisors is an integer number (5325264).

Almost surely, 2^21205739 is an apocalyptic number.

21205739 is a deficient number, since it is larger than the sum of its proper divisors (95317).

21205739 is an equidigital number, since it uses as much as digits as its factorization.

21205739 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 95316.

The product of its (nonzero) digits is 3780, while the sum is 29.

The square root of 21205739 is about 4604.9689466923. The cubic root of 21205739 is about 276.7904726456.

The spelling of 21205739 in words is "twenty-one million, two hundred five thousand, seven hundred thirty-nine".