21351871 has 4 divisors (see below), whose sum is σ = 21361144. Its totient is φ = 21342600.

The previous prime is 21351829. The next prime is 21351893. The reversal of 21351871 is 17815312.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21351871 - 2¹⁷ = 21220799 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 (21351571) 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, 1756 + ... + 6766.

It is an arithmetic number, because the mean of its divisors is an integer number (5340286).

Almost surely, 2^21351871 is an apocalyptic number.

21351871 is a deficient number, since it is larger than the sum of its proper divisors (9273).

21351871 is an equidigital number, since it uses as much as digits as its factorization.

21351871 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9272.

The product of its digits is 1680, while the sum is 28.

The square root of 21351871 is about 4620.8084790435. The cubic root of 21351871 is about 277.4248196091.

It can be divided in two parts, 21351 and 871, that added together give a palindrome (22222).

The spelling of 21351871 in words is "twenty-one million, three hundred fifty-one thousand, eight hundred seventy-one".