646815121920 has 360 divisors, whose sum is σ = 2462272240428. Its totient is φ = 156802990080.

The previous prime is 646815121913. The next prime is 646815121921. The reversal of 646815121920 is 29121518646.

646815121920 is a `hidden beast` number, since 6 + 46 + 8 + 1 + 512 + 1 + 92 + 0 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 643255329024 + 3559792896 = 802032^2 + 59664^2 .

It is a tau number, because it is divible by the number of its divisors (360).

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

It is not an unprimeable number, because it can be changed into a prime (646815121921) by changing a digit.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 2671834 + ... + 2903846.

Almost surely, 2^646815121920 is an apocalyptic number.

646815121920 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 646815121920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1231136120214).

646815121920 is an abundant number, since it is smaller than the sum of its proper divisors (1815457118508).

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

646815121920 is a wasteful number, since it uses less digits than its factorization.

646815121920 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 232064 (or 232034 counting only the distinct ones).

The product of its (nonzero) digits is 207360, while the sum is 45.

The spelling of 646815121920 in words is "six hundred forty-six billion, eight hundred fifteen million, one hundred twenty-one thousand, nine hundred twenty".