21750021 has 12 divisors (see below), whose sum is σ = 33264972. Its totient is φ = 13646976.

The previous prime is 21750017. The next prime is 21750031. The reversal of 21750021 is 12005712.

It can be written as a sum of positive squares in 2 ways, for example, as 6305121 + 15444900 = 2511^2 + 3930^2 .

It is not a de Polignac number, because 21750021 - 2² = 21750017 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21749976 and 21750003.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21750011) 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 11 ways as a sum of consecutive naturals, for example, 70926 + ... + 71231.

It is an arithmetic number, because the mean of its divisors is an integer number (2772081).

Almost surely, 2^21750021 is an apocalyptic number.

It is an amenable number.

21750021 is a deficient number, since it is larger than the sum of its proper divisors (11514951).

21750021 is a wasteful number, since it uses less digits than its factorization.

21750021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 142180 (or 142177 counting only the distinct ones).

The product of its (nonzero) digits is 140, while the sum is 18.

The square root of 21750021 is about 4663.6917779802. The cubic root of 21750021 is about 279.1385984206.

Adding to 21750021 its reverse (12005712), we get a palindrome (33755733).

The spelling of 21750021 in words is "twenty-one million, seven hundred fifty thousand, twenty-one".