81857070720 has 640 divisors, whose sum is σ = 315372657600. Its totient is φ = 20165345280.

The previous prime is 81857070707. The next prime is 81857070733. The reversal of 81857070720 is 2707075818.

81857070720 is a `hidden beast` number, since 8 + 1 + 8 + 570 + 7 + 0 + 72 + 0 = 666.

It is an interprime number because it is at equal distance from previous prime (81857070707) and next prime (81857070733).

It is a tau number, because it is divible by the number of its divisors (640).

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

It is an unprimeable number.

It is a polite number, since it can be written in 79 ways as a sum of consecutive naturals, for example, 40382347 + ... + 40384373.

Almost surely, 2^81857070720 is an apocalyptic number.

81857070720 is a gapful number since it is divisible by the number (80) 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 81857070720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (157686328800).

81857070720 is an abundant number, since it is smaller than the sum of its proper divisors (233515586880).

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

81857070720 is a wasteful number, since it uses less digits than its factorization.

81857070720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2118 (or 2097 counting only the distinct ones).

The product of its (nonzero) digits is 219520, while the sum is 45.

The spelling of 81857070720 in words is "eighty-one billion, eight hundred fifty-seven million, seventy thousand, seven hundred twenty".