6421 has 2 divisors, whose sum is σ = 6422. Its totient is φ = 6420.

The previous prime is 6397. The next prime is 6427. The reversal of 6421 is 1246.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 4900 + 1521 = 70^2 + 39^2 .

It is a cyclic number.

It is not a de Polignac number, because 6421 - 2⁵ = 6389 is a prime.

It is a Chen prime.

It is a plaindrome in base 13.

It is a nialpdrome in base 10.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (6427) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3210 + 3211.

It is an arithmetic number, because the mean of its divisors is an integer number (3211).

It is an amenable number.

6421 is a deficient number, since it is larger than the sum of its proper divisors (1).

6421 is an equidigital number, since it uses as much as digits as its factorization.

6421 is an evil number, because the sum of its binary digits is even.

The product of its digits is 48, while the sum is 13.

The square root of 6421 is about 80.1311425103. The cubic root of 6421 is about 18.5866401153.

Adding to 6421 its reverse (1246), we get a palindrome (7667).

The spelling of 6421 in words is "six thousand, four hundred twenty-one".