21033721 has 2 divisors, whose sum is σ = 21033722. Its totient is φ = 21033720.

The previous prime is 21033667. The next prime is 21033737. The reversal of 21033721 is 12733012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18020025 + 3013696 = 4245^2 + 1736^2 .

It is a cyclic number.

It is not a de Polignac number, because 21033721 - 2¹⁵ = 21000953 is a prime.

It is not a weakly prime, because it can be changed into another prime (21033781) 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 as a sum of consecutive naturals, namely, 10516860 + 10516861.

It is an arithmetic number, because the mean of its divisors is an integer number (10516861).

Almost surely, 2^21033721 is an apocalyptic number.

It is an amenable number.

21033721 is a deficient number, since it is larger than the sum of its proper divisors (1).

21033721 is an equidigital number, since it uses as much as digits as its factorization.

21033721 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 252, while the sum is 19.

The square root of 21033721 is about 4586.2534818738. The cubic root of 21033721 is about 276.0400111776.

Adding to 21033721 its reverse (12733012), we get a palindrome (33766733).

The spelling of 21033721 in words is "twenty-one million, thirty-three thousand, seven hundred twenty-one".