21731977 has 4 divisors (see below), whose sum is σ = 21956116. Its totient is φ = 21507840.

The previous prime is 21731971. The next prime is 21731981. The reversal of 21731977 is 77913712.

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

It can be written as a sum of positive squares in 2 ways, for example, as 9369721 + 12362256 = 3061^2 + 3516^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21731977 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21731971) 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, 111924 + ... + 112117.

It is an arithmetic number, because the mean of its divisors is an integer number (5489029).

Almost surely, 2^21731977 is an apocalyptic number.

It is an amenable number.

21731977 is a deficient number, since it is larger than the sum of its proper divisors (224139).

21731977 is an equidigital number, since it uses as much as digits as its factorization.

21731977 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 224138.

The product of its digits is 18522, while the sum is 37.

The square root of 21731977 is about 4661.7568576664. The cubic root of 21731977 is about 279.0613851562.

The spelling of 21731977 in words is "twenty-one million, seven hundred thirty-one thousand, nine hundred seventy-seven".