421840 has 20 divisors (see below), whose sum is σ = 980964. Its totient is φ = 168704.

The previous prime is 421831. The next prime is 421847. The reversal of 421840 is 48124.

It can be written as a sum of positive squares in 2 ways, for example, as 179776 + 242064 = 424^2 + 492^2 .

It is a tau number, because it is divible by the number of its divisors (20).

It is an Ulam number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (421847) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2557 + ... + 2716.

2⁴²¹⁸⁴⁰ is an apocalyptic number.

421840 is a gapful number since it is divisible by the number (40) formed by its first and last digit.

It is an amenable number.

421840 is an abundant number, since it is smaller than the sum of its proper divisors (559124).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

421840 is a wasteful number, since it uses less digits than its factorization.

421840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5286 (or 5280 counting only the distinct ones).

The product of its (nonzero) digits is 256, while the sum is 19.

The square root of 421840 is about 649.4921092669. The cubic root of 421840 is about 74.9979258686.

Subtracting from 421840 its sum of digits (19), we obtain a triangular number (421821 = T₉₁₈).

Adding to 421840 its reverse (48124), we get a palindrome (469964).

The spelling of 421840 in words is "four hundred twenty-one thousand, eight hundred forty".