21003871 has 4 divisors (see below), whose sum is σ = 24004432. Its totient is φ = 18003312.

The previous prime is 21003869. The next prime is 21003883. The reversal of 21003871 is 17830012.

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 21003871 - 2¹ = 21003869 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 (21003811) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1500270 + ... + 1500283.

It is an arithmetic number, because the mean of its divisors is an integer number (6001108).

Almost surely, 2^21003871 is an apocalyptic number.

21003871 is a deficient number, since it is larger than the sum of its proper divisors (3000561).

21003871 is an equidigital number, since it uses as much as digits as its factorization.

21003871 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3000560.

The product of its (nonzero) digits is 336, while the sum is 22.

The square root of 21003871 is about 4582.9980362204. The cubic root of 21003871 is about 275.9093686529.

Adding to 21003871 its reverse (17830012), we get a palindrome (38833883).

The spelling of 21003871 in words is "twenty-one million, three thousand, eight hundred seventy-one".