21108749 has 2 divisors, whose sum is σ = 21108750. Its totient is φ = 21108748.

The previous prime is 21108707. The next prime is 21108751. The reversal of 21108749 is 94780112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16728100 + 4380649 = 4090^2 + 2093^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21108749 is a prime.

Together with 21108751, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21108349) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10554374 + 10554375.

It is an arithmetic number, because the mean of its divisors is an integer number (10554375).

Almost surely, 2^21108749 is an apocalyptic number.

It is an amenable number.

21108749 is a deficient number, since it is larger than the sum of its proper divisors (1).

21108749 is an equidigital number, since it uses as much as digits as its factorization.

21108749 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 4032, while the sum is 32.

The square root of 21108749 is about 4594.4258618461. The cubic root of 21108749 is about 276.3678364088.

The spelling of 21108749 in words is "twenty-one million, one hundred eight thousand, seven hundred forty-nine".