21305771 has 4 divisors (see below), whose sum is σ = 21332544. Its totient is φ = 21279000.

The previous prime is 21305761. The next prime is 21305789. The reversal of 21305771 is 17750312.

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

It is a cyclic number.

It is not a de Polignac number, because 21305771 - 2¹⁰ = 21304747 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21305771.

It is not an unprimeable number, because it can be changed into a prime (21305741) 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, 12155 + ... + 13796.

It is an arithmetic number, because the mean of its divisors is an integer number (5333136).

Almost surely, 2^21305771 is an apocalyptic number.

21305771 is a deficient number, since it is larger than the sum of its proper divisors (26773).

21305771 is an equidigital number, since it uses as much as digits as its factorization.

21305771 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 26772.

The product of its (nonzero) digits is 1470, while the sum is 26.

The square root of 21305771 is about 4615.8174790605. The cubic root of 21305771 is about 277.2250166734.

The spelling of 21305771 in words is "twenty-one million, three hundred five thousand, seven hundred seventy-one".