645978 has 32 divisors (see below), whose sum is σ = 1400832. Its totient is φ = 198000.

The previous prime is 645973. The next prime is 645979. The reversal of 645978 is 879546.

645978 is nontrivially palindromic in base 8.

Its product of digits (60480) is a multiple of the sum of its prime divisors (210).

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (645973) by changing a digit.

645978 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 15 ways as a sum of consecutive naturals, for example, 4203 + ... + 4353.

It is an arithmetic number, because the mean of its divisors is an integer number (43776).

2⁶⁴⁵⁹⁷⁸ is an apocalyptic number.

645978 is an abundant number, since it is smaller than the sum of its proper divisors (754854).

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

645978 is a wasteful number, since it uses less digits than its factorization.

645978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 210.

The product of its digits is 60480, while the sum is 39.

The square root of 645978 is about 803.7275657833. The cubic root of 645978 is about 86.4448733808. Note that the first 3 decimals are identical.

The spelling of 645978 in words is "six hundred forty-five thousand, nine hundred seventy-eight".