21751321 has 4 divisors (see below), whose sum is σ = 21762100. Its totient is φ = 21740544.

The previous prime is 21751291. The next prime is 21751337. The reversal of 21751321 is 12315712.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 490000 + 21261321 = 700^2 + 4611^2 .

It is a cyclic number.

It is not a de Polignac number, because 21751321 - 2⁷ = 21751193 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21751292 and 21751301.

It is not an unprimeable number, because it can be changed into a prime (21751351) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1356 + ... + 6733.

It is an arithmetic number, because the mean of its divisors is an integer number (5440525).

Almost surely, 2^21751321 is an apocalyptic number.

It is an amenable number.

21751321 is a deficient number, since it is larger than the sum of its proper divisors (10779).

21751321 is an equidigital number, since it uses as much as digits as its factorization.

21751321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10778.

The product of its digits is 420, while the sum is 22.

The square root of 21751321 is about 4663.8311504599. The cubic root of 21751321 is about 279.1441596864.

The spelling of 21751321 in words is "twenty-one million, seven hundred fifty-one thousand, three hundred twenty-one".