645205431780 has 432 divisors, whose sum is σ = 2549491701120. Its totient is φ = 128965644288.

The previous prime is 645205431751. The next prime is 645205431811. The reversal of 645205431780 is 87134502546.

645205431780 is a `hidden beast` number, since 6 + 4 + 5 + 20 + 543 + 1 + 7 + 80 = 666.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is an unprimeable number.

It is a polite number, since it can be written in 143 ways as a sum of consecutive naturals, for example, 3966124 + ... + 4125596.

It is an arithmetic number, because the mean of its divisors is an integer number (5901601160).

Almost surely, 2^645205431780 is an apocalyptic number.

645205431780 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 645205431780, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1274745850560).

645205431780 is an abundant number, since it is smaller than the sum of its proper divisors (1904286269340).

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

645205431780 is a wasteful number, since it uses less digits than its factorization.

645205431780 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 159540 (or 159522 counting only the distinct ones).

The product of its (nonzero) digits is 806400, while the sum is 45.

The spelling of 645205431780 in words is "six hundred forty-five billion, two hundred five million, four hundred thirty-one thousand, seven hundred eighty".