861821640 has 128 divisors (see below), whose sum is σ = 2942956800. Its totient is φ = 224202240.

The previous prime is 861821629. The next prime is 861821641. The reversal of 861821640 is 46128168.

861821640 is a `hidden beast` number, since 8 + 6 + 1 + 8 + 2 + 1 + 640 = 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 = 861821595 and 861821604.

It is not an unprimeable number, because it can be changed into a prime (861821641) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 34549 + ... + 54011.

It is an arithmetic number, because the mean of its divisors is an integer number (22991850).

Almost surely, 2^861821640 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 861821640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1471478400).

861821640 is an abundant number, since it is smaller than the sum of its proper divisors (2081135160).

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

861821640 is a wasteful number, since it uses less digits than its factorization.

861821640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19524 (or 19514 counting only the distinct ones).

The product of its (nonzero) digits is 18432, while the sum is 36.

The square root of 861821640 is about 29356.7988718116. The cubic root of 861821640 is about 951.6395105476.

The spelling of 861821640 in words is "eight hundred sixty-one million, eight hundred twenty-one thousand, six hundred forty".