21771 has 12 divisors (see below), whose sum is σ = 32760. Its totient is φ = 13920.

The previous prime is 21767. The next prime is 21773. The reversal of 21771 is 17712.

It is not a de Polignac number, because 21771 - 2² = 21767 is a prime.

21771 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (21773) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 340 + ... + 398.

It is an arithmetic number, because the mean of its divisors is an integer number (2730).

2²¹⁷⁷¹ is an apocalyptic number.

21771 is a deficient number, since it is larger than the sum of its proper divisors (10989).

21771 is a wasteful number, since it uses less digits than its factorization.

21771 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 106 (or 103 counting only the distinct ones).

The product of its digits is 98, while the sum is 18.

The square root of 21771 is about 147.5499915283. The cubic root of 21771 is about 27.9228317366.

The spelling of 21771 in words is "twenty-one thousand, seven hundred seventy-one", and thus it is an iban number.