640039400 has 384 divisors, whose sum is σ = 2099865600. Its totient is φ = 174873600.

The previous prime is 640039333. The next prime is 640039427. The reversal of 640039400 is 4930046.

It is a Cunningham number, because it is equal to 25299²-1.

It is a Harshad number since it is a multiple of its sum of digits (26).

It is a self number, because there is not a number n which added to its sum of digits gives 640039400.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 4604531 + ... + 4604669.

It is an arithmetic number, because the mean of its divisors is an integer number (5468400).

Almost surely, 2^640039400 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 640039400, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1049932800).

640039400 is an abundant number, since it is smaller than the sum of its proper divisors (1459826200).

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

640039400 is a wasteful number, since it uses less digits than its factorization.

640039400 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 209 (or 200 counting only the distinct ones).

The product of its (nonzero) digits is 2592, while the sum is 26.

The square root of 640039400 is about 25298.9999802364. Note that the first 4 decimals coincide. The cubic root of 640039400 is about 861.7915599679.

Adding to 640039400 its reverse (4930046), we get a palindrome (644969446).

The spelling of 640039400 in words is "six hundred forty million, thirty-nine thousand, four hundred".