21018247 has 2 divisors, whose sum is σ = 21018248. Its totient is φ = 21018246.

The previous prime is 21018241. The next prime is 21018287. The reversal of 21018247 is 74281012.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21018247 - 2¹⁵ = 20985479 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21018241) 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, 10509123 + 10509124.

It is an arithmetic number, because the mean of its divisors is an integer number (10509124).

Almost surely, 2^21018247 is an apocalyptic number.

21018247 is a deficient number, since it is larger than the sum of its proper divisors (1).

21018247 is an equidigital number, since it uses as much as digits as its factorization.

21018247 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 896, while the sum is 25.

The square root of 21018247 is about 4584.5661735872. The cubic root of 21018247 is about 275.9723025836.

Adding to 21018247 its reverse (74281012), we get a palindrome (95299259).

The spelling of 21018247 in words is "twenty-one million, eighteen thousand, two hundred forty-seven".