21000871 has 4 divisors (see below), whose sum is σ = 22106200. Its totient is φ = 19895544.

The previous prime is 21000853. The next prime is 21000883. The reversal of 21000871 is 17800012.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21000871 - 2⁵ = 21000839 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (19), and also a Moran number because the ratio is a prime number: 1105309 = 21000871 / (2 + 1 + 0 + 0 + 0 + 8 + 7 + 1).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21000821) 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 in 3 ways as a sum of consecutive naturals, for example, 552636 + ... + 552673.

It is an arithmetic number, because the mean of its divisors is an integer number (5526550).

Almost surely, 2^21000871 is an apocalyptic number.

21000871 is a deficient number, since it is larger than the sum of its proper divisors (1105329).

21000871 is a wasteful number, since it uses less digits than its factorization.

21000871 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1105328.

The product of its (nonzero) digits is 112, while the sum is 19.

The square root of 21000871 is about 4582.6707278616. The cubic root of 21000871 is about 275.8962319075.

Adding to 21000871 its reverse (17800012), we get a palindrome (38800883).

The spelling of 21000871 in words is "twenty-one million, eight hundred seventy-one", and thus it is an aban number.