640998 has 24 divisors (see below), whose sum is σ = 1404000. Its totient is φ = 211344.

The previous prime is 640993. The next prime is 641051. The reversal of 640998 is 899046.

640998 is a `hidden beast` number, since 640 + 9 + 9 + 8 = 666.

It is a Smith number, since the sum of its digits (36) coincides with the sum of the digits of its prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640993) by changing a digit.

640998 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 11 ways as a sum of consecutive naturals, for example, 2563 + ... + 2801.

It is an arithmetic number, because the mean of its divisors is an integer number (58500).

2⁶⁴⁰⁹⁹⁸ is an apocalyptic number.

640998 is an abundant number, since it is smaller than the sum of its proper divisors (763002).

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

640998 is a wasteful number, since it uses less digits than its factorization.

640998 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 396 (or 393 counting only the distinct ones).

The product of its (nonzero) digits is 15552, while the sum is 36.

The square root of 640998 is about 800.6235070244. The cubic root of 640998 is about 86.2221586257. Note that the first 3 decimals are identical.

The spelling of 640998 in words is "six hundred forty thousand, nine hundred ninety-eight".