645621256566 has 96 divisors (see below), whose sum is σ = 1645748526240. Its totient is φ = 180335232000.

The previous prime is 645621256559. The next prime is 645621256601. The reversal of 645621256566 is 665652126546.

It is a happy number.

645621256566 is a `hidden beast` number, since 6 + 4 + 5 + 6 + 2 + 12 + 565 + 66 = 666.

It is a super-2 number, since 2×645621256566² (a number of 24 digits) contains 22 as substring.

It is a Smith number, since the sum of its digits (54) coincides with the sum of the digits of its prime factors.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 1625470 + ... + 1983278.

It is an arithmetic number, because the mean of its divisors is an integer number (17143213815).

Almost surely, 2^645621256566 is an apocalyptic number.

645621256566 is a gapful number since it is divisible by the number (66) formed by its first and last digit.

It is a practical number, because each smaller number is the sum of distinct divisors of 645621256566, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (822874263120).

645621256566 is an abundant number, since it is smaller than the sum of its proper divisors (1000127269674).

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

645621256566 is a wasteful number, since it uses less digits than its factorization.

645621256566 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 358542 (or 358539 counting only the distinct ones).

The product of its digits is 15552000, while the sum is 54.

The spelling of 645621256566 in words is "six hundred forty-five billion, six hundred twenty-one million, two hundred fifty-six thousand, five hundred sixty-six".