21953 has 4 divisors (see below), whose sum is σ = 22740. Its totient is φ = 21168.

The previous prime is 21943. The next prime is 21961. The reversal of 21953 is 35912.

It is a Cunningham number, because it is equal to 28³+1.

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 12544 + 9409 = 112^2 + 97^2 .

It is a cyclic number.

It is not a de Polignac number, because 21953 - 2⁴ = 21937 is a prime.

It is a Duffinian number.

It is a plaindrome in base 15.

It is not an unprimeable number, because it can be changed into a prime (21943) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 350 + ... + 407.

It is an arithmetic number, because the mean of its divisors is an integer number (5685).

21953 is a Friedman number, since it can be written as ((9+5)*2)^3+1, using all its digits and the basic arithmetic operations.

2²¹⁹⁵³ is an apocalyptic number.

It is an amenable number.

21953 is a deficient number, since it is larger than the sum of its proper divisors (787).

21953 is an equidigital number, since it uses as much as digits as its factorization.

21953 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 786.

The product of its digits is 270, while the sum is 20.

The square root of 21953 is about 148.1654480640. The cubic root of 21953 is about 28.0004251636. Note that the first 3 decimals are identical.

It can be divided in two parts, 219 and 53, that added together give a palindrome (272).

The spelling of 21953 in words is "twenty-one thousand, nine hundred fifty-three".