645656220 has 288 divisors, whose sum is σ = 2252630016. Its totient is φ = 148262400.

The previous prime is 645656201. The next prime is 645656239. The reversal of 645656220 is 22656546.

645656220 is a `hidden beast` number, since 645 + 6 + 5 + 6 + 2 + 2 + 0 = 666.

It is an interprime number because it is at equal distance from previous prime (645656201) and next prime (645656239).

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

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 4112382 + ... + 4112538.

It is an arithmetic number, because the mean of its divisors is an integer number (7821632).

Almost surely, 2^645656220 is an apocalyptic number.

645656220 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 645656220, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1126315008).

645656220 is an abundant number, since it is smaller than the sum of its proper divisors (1606973796).

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

645656220 is a wasteful number, since it uses less digits than its factorization.

645656220 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 281 (or 276 counting only the distinct ones).

The product of its (nonzero) digits is 86400, while the sum is 36.

The square root of 645656220 is about 25409.7662326909. The cubic root of 645656220 is about 864.3051744751.

The spelling of 645656220 in words is "six hundred forty-five million, six hundred fifty-six thousand, two hundred twenty".