8421 has 8 divisors (see below), whose sum is σ = 12864. Its totient is φ = 4800.

The previous prime is 8419. The next prime is 8423. The reversal of 8421 is 1248.

It is an interprime number because it is at equal distance from previous prime (8419) and next prime (8423).

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

It is not a de Polignac number, because 8421 - 2¹ = 8419 is a prime.

It is a Smith number, since the sum of its digits (15) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is an Ulam number.

It is a Curzon number.

8421 is a lucky number.

It is a plaindrome in base 13.

It is a nialpdrome in base 10.

It is a self number, because there is not a number n which added to its sum of digits gives 8421.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (8423) by changing a digit.

It is a nontrivial repunit in base 20.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 180 + ... + 221.

It is an arithmetic number, because the mean of its divisors is an integer number (1608).

2⁸⁴²¹ is an apocalyptic number.

It is an amenable number.

8421 is a deficient number, since it is larger than the sum of its proper divisors (4443).

8421 is a wasteful number, since it uses less digits than its factorization.

8421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 411.

The product of its digits is 64, while the sum is 15.

The square root of 8421 is about 91.7660067781. The cubic root of 8421 is about 20.3448529785.

Adding to 8421 its reverse (1248), we get a palindrome (9669).

It can be divided in two parts, 84 and 21, that multiplied together give a square (1764 = 42²).

The spelling of 8421 in words is "eight thousand, four hundred twenty-one".