21005247 has 8 divisors (see below), whose sum is σ = 28099456. Its totient is φ = 13957272.

The previous prime is 21005227. The next prime is 21005269. The reversal of 21005247 is 74250012.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21005247 - 2¹⁸ = 20743103 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21005227) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 10483 + ... + 12324.

It is an arithmetic number, because the mean of its divisors is an integer number (3512432).

Almost surely, 2^21005247 is an apocalyptic number.

21005247 is a deficient number, since it is larger than the sum of its proper divisors (7094209).

21005247 is a wasteful number, since it uses less digits than its factorization.

21005247 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23117.

The product of its (nonzero) digits is 560, while the sum is 21.

The square root of 21005247 is about 4583.1481538349. The cubic root of 21005247 is about 275.9153936217.

Adding to 21005247 its reverse (74250012), we get a palindrome (95255259).

The spelling of 21005247 in words is "twenty-one million, five thousand, two hundred forty-seven".