640400420 has 24 divisors (see below), whose sum is σ = 1467099648. Its totient is φ = 232872800.

The previous prime is 640400401. The next prime is 640400429. The reversal of 640400420 is 24004046.

It is a super-2 number, since 2×640400420² = 820225395872352800, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (20).

It is a junction number, because it is equal to n+sod(n) for n = 640400392 and 640400401.

It is not an unprimeable number, because it can be changed into a prime (640400429) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1455236 + ... + 1455675.

It is an arithmetic number, because the mean of its divisors is an integer number (61129152).

Almost surely, 2^640400420 is an apocalyptic number.

It is an amenable number.

640400420 is an abundant number, since it is smaller than the sum of its proper divisors (826699228).

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

640400420 is a wasteful number, since it uses less digits than its factorization.

640400420 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2910931 (or 2910929 counting only the distinct ones).

The product of its (nonzero) digits is 768, while the sum is 20.

The square root of 640400420 is about 25306.1340390033. The cubic root of 640400420 is about 861.9535632810.

Adding to 640400420 its reverse (24004046), we get a palindrome (664404466).

The spelling of 640400420 in words is "six hundred forty million, four hundred thousand, four hundred twenty".