21750081 has 4 divisors (see below), whose sum is σ = 29000112. Its totient is φ = 14500052.

The previous prime is 21750077. The next prime is 21750083. The reversal of 21750081 is 18005712.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21750081 - 2² = 21750077 is a prime.

It is a super-2 number, since 2×21750081² = 946132047013122, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21750083) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3625011 + ... + 3625016.

It is an arithmetic number, because the mean of its divisors is an integer number (7250028).

Almost surely, 2^21750081 is an apocalyptic number.

It is an amenable number.

21750081 is a deficient number, since it is larger than the sum of its proper divisors (7250031).

21750081 is an equidigital number, since it uses as much as digits as its factorization.

21750081 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7250030.

The product of its (nonzero) digits is 560, while the sum is 24.

The square root of 21750081 is about 4663.6982106479. The cubic root of 21750081 is about 279.1388550993.

Adding to 21750081 its reverse (18005712), we get a palindrome (39755793).

The spelling of 21750081 in words is "twenty-one million, seven hundred fifty thousand, eighty-one".