21785849 has 2 divisors, whose sum is σ = 21785850. Its totient is φ = 21785848.

The previous prime is 21785843. The next prime is 21785851. The reversal of 21785849 is 94858712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15460624 + 6325225 = 3932^2 + 2515^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21785849 is a prime.

Together with 21785851, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21785843) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10892924 + 10892925.

It is an arithmetic number, because the mean of its divisors is an integer number (10892925).

Almost surely, 2^21785849 is an apocalyptic number.

It is an amenable number.

21785849 is a deficient number, since it is larger than the sum of its proper divisors (1).

21785849 is an equidigital number, since it uses as much as digits as its factorization.

21785849 is an evil number, because the sum of its binary digits is even.

The product of its digits is 161280, while the sum is 44.

The square root of 21785849 is about 4667.5313603660. The cubic root of 21785849 is about 279.2917858790.

The spelling of 21785849 in words is "twenty-one million, seven hundred eighty-five thousand, eight hundred forty-nine".