21577 has 2 divisors, whose sum is σ = 21578. Its totient is φ = 21576.

The previous prime is 21569. The next prime is 21587. The reversal of 21577 is 77512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20736 + 841 = 144^2 + 29^2 .

It is a cyclic number.

It is not a de Polignac number, because 21577 - 2³ = 21569 is a prime.

It is a Chen prime.

It is a nialpdrome in base 8.

It is not a weakly prime, because it can be changed into another prime (21517) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10788 + 10789.

It is an arithmetic number, because the mean of its divisors is an integer number (10789).

2²¹⁵⁷⁷ is an apocalyptic number.

It is an amenable number.

21577 is a deficient number, since it is larger than the sum of its proper divisors (1).

21577 is an equidigital number, since it uses as much as digits as its factorization.

21577 is an evil number, because the sum of its binary digits is even.

The product of its digits is 490, while the sum is 22.

The square root of 21577 is about 146.8911161371. The cubic root of 21577 is about 27.8396446260.

It can be divided in two parts, 215 and 77, that added together give a palindrome (292).

The spelling of 21577 in words is "twenty-one thousand, five hundred seventy-seven".