645661440 has 216 divisors, whose sum is σ = 2290081248. Its totient is φ = 167854080.

The previous prime is 645661369. The next prime is 645661531. The reversal of 645661440 is 44166546.

645661440 is a `hidden beast` number, since 645 + 6 + 6 + 1 + 4 + 4 + 0 = 666.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 645661395 and 645661404.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 471637 + ... + 473003.

It is an arithmetic number, because the mean of its divisors is an integer number (10602228).

Almost surely, 2^645661440 is an apocalyptic number.

645661440 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 645661440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1145040624).

645661440 is an abundant number, since it is smaller than the sum of its proper divisors (1644419808).

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

645661440 is a wasteful number, since it uses less digits than its factorization.

645661440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1435 (or 1418 counting only the distinct ones).

The product of its (nonzero) digits is 69120, while the sum is 36.

The square root of 645661440 is about 25409.8689488946. The cubic root of 645661440 is about 864.3075037130.

It can be divided in two parts, 6456 and 61440, that added together give a triangular number (67896 = T₃₆₈).

The spelling of 645661440 in words is "six hundred forty-five million, six hundred sixty-one thousand, four hundred forty".