21005847 has 18 divisors (see below), whose sum is σ = 30841616. Its totient is φ = 13776840.

The previous prime is 21005837. The next prime is 21005857. The reversal of 21005847 is 74850012.

It is an interprime number because it is at equal distance from previous prime (21005837) and next prime (21005857).

It is not a de Polignac number, because 21005847 - 2¹⁸ = 20743703 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21005847.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21005807) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 45138 + ... + 45600.

Almost surely, 2^21005847 is an apocalyptic number.

21005847 is a deficient number, since it is larger than the sum of its proper divisors (9835769).

21005847 is an equidigital number, since it uses as much as digits as its factorization.

21005847 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 611 (or 537 counting only the distinct ones).

The product of its (nonzero) digits is 2240, while the sum is 27.

The square root of 21005847 is about 4583.2136105576. The cubic root of 21005847 is about 275.9180207060.

Adding to 21005847 its reverse (74850012), we get a palindrome (95855859).

The spelling of 21005847 in words is "twenty-one million, five thousand, eight hundred forty-seven".