640400 has 30 divisors (see below), whose sum is σ = 1539522. Its totient is φ = 256000.

The previous prime is 640369. The next prime is 640411. The reversal of 640400 is 4046.

It is a happy number.

It can be written as a sum of positive squares in 3 ways, for example, as 215296 + 425104 = 464^2 + 652^2 .

It is a super-2 number, since 2×640400² = 820224320000, which contains 22 as substring.

It is an unprimeable number.

640400 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 401 + ... + 1200.

2⁶⁴⁰⁴⁰⁰ is an apocalyptic number.

It is an amenable number.

640400 is an abundant number, since it is smaller than the sum of its proper divisors (899122).

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

640400 is a wasteful number, since it uses less digits than its factorization.

640400 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1619 (or 1608 counting only the distinct ones).

The product of its (nonzero) digits is 96, while the sum is 14.

The square root of 640400 is about 800.2499609497. The cubic root of 640400 is about 86.1953374847.

Adding to 640400 its reverse (4046), we get a palindrome (644446).

The spelling of 640400 in words is "six hundred forty thousand, four hundred".