21992 has 8 divisors (see below), whose sum is σ = 41250. Its totient is φ = 10992.

The previous prime is 21991. The next prime is 21997. The reversal of 21992 is 29912.

It can be written as a sum of positive squares in only one way, i.e., 21316 + 676 = 146^2 + 26^2 .

It is a tau number, because it is divible by the number of its divisors (8).

It is an Ulam number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 21992.

It is not an unprimeable number, because it can be changed into a prime (21991) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1367 + ... + 1382.

2²¹⁹⁹² is an apocalyptic number.

It is an amenable number.

21992 is a deficient number, since it is larger than the sum of its proper divisors (19258).

21992 is a wasteful number, since it uses less digits than its factorization.

21992 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2755 (or 2751 counting only the distinct ones).

The product of its digits is 324, while the sum is 23.

The square root of 21992 is about 148.2969992953. The cubic root of 21992 is about 28.0169964835.

The spelling of 21992 in words is "twenty-one thousand, nine hundred ninety-two".