20721749 has 2 divisors, whose sum is σ = 20721750. Its totient is φ = 20721748.

The previous prime is 20721737. The next prime is 20721763. The reversal of 20721749 is 94712702.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12780625 + 7941124 = 3575^2 + 2818^2 .

It is a cyclic number.

It is not a de Polignac number, because 20721749 - 2¹⁶ = 20656213 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20721719) 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 as a sum of consecutive naturals, namely, 10360874 + 10360875.

It is an arithmetic number, because the mean of its divisors is an integer number (10360875).

Almost surely, 2^20721749 is an apocalyptic number.

It is an amenable number.

20721749 is a deficient number, since it is larger than the sum of its proper divisors (1).

20721749 is an equidigital number, since it uses as much as digits as its factorization.

20721749 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 7056, while the sum is 32.

The square root of 20721749 is about 4552.1147832628. The cubic root of 20721749 is about 274.6684665876.

The spelling of 20721749 in words is "twenty million, seven hundred twenty-one thousand, seven hundred forty-nine".