21708749 has 2 divisors, whose sum is σ = 21708750. Its totient is φ = 21708748.

The previous prime is 21708727. The next prime is 21708761. The reversal of 21708749 is 94780712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20994724 + 714025 = 4582^2 + 845^2 .

It is a cyclic number.

It is not a de Polignac number, because 21708749 - 2¹² = 21704653 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 (21701749) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10854374 + 10854375.

It is an arithmetic number, because the mean of its divisors is an integer number (10854375).

Almost surely, 2^21708749 is an apocalyptic number.

It is an amenable number.

21708749 is a deficient number, since it is larger than the sum of its proper divisors (1).

21708749 is an equidigital number, since it uses as much as digits as its factorization.

21708749 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 28224, while the sum is 38.

The square root of 21708749 is about 4659.2648561763. The cubic root of 21708749 is about 278.9619257491.

The spelling of 21708749 in words is "twenty-one million, seven hundred eight thousand, seven hundred forty-nine".