21722 has 4 divisors (see below), whose sum is σ = 32586. Its totient is φ = 10860.

The previous prime is 21713. The next prime is 21727. The reversal of 21722 is 22712.

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

It can be written as a sum of positive squares in only one way, i.e., 19321 + 2401 = 139^2 + 49^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21697 and 21706.

It is not an unprimeable number, because it can be changed into a prime (21727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5429 + ... + 5432.

2²¹⁷²² is an apocalyptic number.

21722 is a deficient number, since it is larger than the sum of its proper divisors (10864).

21722 is a wasteful number, since it uses less digits than its factorization.

21722 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10863.

The product of its digits is 56, while the sum is 14.

The square root of 21722 is about 147.3838525755. The cubic root of 21722 is about 27.9018673570.

Adding to 21722 its sum of digits (14), we get a triangular number (21736 = T₂₀₈).

Subtracting 21722 from its reverse (22712), we obtain a triangular number (990 = T₄₄).

It can be divided in two parts, 217 and 22, that multiplied together give a palindrome (4774).

The spelling of 21722 in words is "twenty-one thousand, seven hundred twenty-two", and thus it is an iban number.