420821 has 4 divisors (see below), whose sum is σ = 422592. Its totient is φ = 419052.

The previous prime is 420811. The next prime is 420851. The reversal of 420821 is 128024.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 420821 - 2⁶ = 420757 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 420821.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (420811) 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, 461 + ... + 1026.

It is an arithmetic number, because the mean of its divisors is an integer number (105648).

2⁴²⁰⁸²¹ is an apocalyptic number.

It is an amenable number.

420821 is a deficient number, since it is larger than the sum of its proper divisors (1771).

420821 is a wasteful number, since it uses less digits than its factorization.

420821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1770.

The product of its (nonzero) digits is 128, while the sum is 17.

The square root of 420821 is about 648.7071758506. The cubic root of 420821 is about 74.9374886530.

Adding to 420821 its reverse (128024), we get a palindrome (548845).

The spelling of 420821 in words is "four hundred twenty thousand, eight hundred twenty-one".