21005245 has 8 divisors (see below), whose sum is σ = 25277184. Its totient is φ = 16756944.

The previous prime is 21005227. The next prime is 21005269. The reversal of 21005245 is 54250012.

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

It is a cyclic number.

It is not a de Polignac number, because 21005245 - 2¹⁷ = 20874173 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

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 in 7 ways as a sum of consecutive naturals, for example, 3889 + ... + 7558.

It is an arithmetic number, because the mean of its divisors is an integer number (3159648).

Almost surely, 2^21005245 is an apocalyptic number.

It is an amenable number.

21005245 is a deficient number, since it is larger than the sum of its proper divisors (4271939).

21005245 is a wasteful number, since it uses less digits than its factorization.

21005245 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11819.

The product of its (nonzero) digits is 400, while the sum is 19.

The square root of 21005245 is about 4583.1479356442. The cubic root of 21005245 is about 275.9153848647.

Adding to 21005245 its reverse (54250012), we get a palindrome (75255257).

The spelling of 21005245 in words is "twenty-one million, five thousand, two hundred forty-five".