21705241 has 2 divisors, whose sum is σ = 21705242. Its totient is φ = 21705240.

The previous prime is 21705227. The next prime is 21705269. The reversal of 21705241 is 14250712.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20025625 + 1679616 = 4475^2 + 1296^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21705241 is a prime.

It is a super-2 number, since 2×21705241² = 942234973736162, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21705041) 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, 10852620 + 10852621.

It is an arithmetic number, because the mean of its divisors is an integer number (10852621).

Almost surely, 2^21705241 is an apocalyptic number.

It is an amenable number.

21705241 is a deficient number, since it is larger than the sum of its proper divisors (1).

21705241 is an equidigital number, since it uses as much as digits as its factorization.

21705241 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 560, while the sum is 22.

The square root of 21705241 is about 4658.8883867292. Note that the first 3 decimals coincide. The cubic root of 21705241 is about 278.9468987638.

Adding to 21705241 its reverse (14250712), we get a palindrome (35955953).

The spelling of 21705241 in words is "twenty-one million, seven hundred five thousand, two hundred forty-one".