21006247 has 2 divisors, whose sum is σ = 21006248. Its totient is φ = 21006246.

The previous prime is 21006239. The next prime is 21006257. The reversal of 21006247 is 74260012.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21006247 - 2³ = 21006239 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21006217) 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, 10503123 + 10503124.

It is an arithmetic number, because the mean of its divisors is an integer number (10503124).

Almost surely, 2^21006247 is an apocalyptic number.

21006247 is a deficient number, since it is larger than the sum of its proper divisors (1).

21006247 is an equidigital number, since it uses as much as digits as its factorization.

21006247 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 672, while the sum is 22.

The square root of 21006247 is about 4583.2572478533. The cubic root of 21006247 is about 275.9197720677.

Adding to 21006247 its reverse (74260012), we get a palindrome (95266259).

The spelling of 21006247 in words is "twenty-one million, six thousand, two hundred forty-seven".