21977 has 2 divisors, whose sum is σ = 21978. Its totient is φ = 21976.

The previous prime is 21961. The next prime is 21991. The reversal of 21977 is 77912.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18496 + 3481 = 136^2 + 59^2 .

It is a cyclic number.

It is not a de Polignac number, because 21977 - 2⁴ = 21961 is a prime.

It is a Chen prime.

It is a plaindrome in base 11.

It is not a weakly prime, because it can be changed into another prime (21937) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10988 + 10989.

It is an arithmetic number, because the mean of its divisors is an integer number (10989).

2²¹⁹⁷⁷ is an apocalyptic number.

It is an amenable number.

21977 is a deficient number, since it is larger than the sum of its proper divisors (1).

21977 is an equidigital number, since it uses as much as digits as its factorization.

21977 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 882, while the sum is 26.

The square root of 21977 is about 148.2464164828. The cubic root of 21977 is about 28.0106252192.

The spelling of 21977 in words is "twenty-one thousand, nine hundred seventy-seven".