21785749 has 2 divisors, whose sum is σ = 21785750. Its totient is φ = 21785748.

The previous prime is 21785747. The next prime is 21785767. The reversal of 21785749 is 94758712.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18861649 + 2924100 = 4343^2 + 1710^2 .

It is a cyclic number.

It is not a de Polignac number, because 21785749 - 2¹ = 21785747 is a prime.

Together with 21785747, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21785741) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10892874 + 10892875.

It is an arithmetic number, because the mean of its divisors is an integer number (10892875).

Almost surely, 2^21785749 is an apocalyptic number.

It is an amenable number.

21785749 is a deficient number, since it is larger than the sum of its proper divisors (1).

21785749 is an equidigital number, since it uses as much as digits as its factorization.

21785749 is an evil number, because the sum of its binary digits is even.

The product of its digits is 141120, while the sum is 43.

The square root of 21785749 is about 4667.5206480529. The cubic root of 21785749 is about 279.2913585493.

The spelling of 21785749 in words is "twenty-one million, seven hundred eighty-five thousand, seven hundred forty-nine".