81636971850 has 360 divisors, whose sum is σ = 266541213708. Its totient is φ = 18470592000.

The previous prime is 81636971849. The next prime is 81636971861. The reversal of 81636971850 is 5817963618.

It can be written as a sum of positive squares in 6 ways, for example, as 34751297889 + 46885673961 = 186417^2 + 216531^2 .

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 Harshad number since it is a multiple of its sum of digits (54).

It is an unprimeable number.

It is a polite number, since it can be written in 179 ways as a sum of consecutive naturals, for example, 20041414 + ... + 20045486.

Almost surely, 2^81636971850 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81636971850, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (133270606854).

81636971850 is an abundant number, since it is smaller than the sum of its proper divisors (184904241858).

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

81636971850 is a wasteful number, since it uses less digits than its factorization.

81636971850 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4212 (or 4191 counting only the distinct ones).

The product of its (nonzero) digits is 2177280, while the sum is 54.

The spelling of 81636971850 in words is "eighty-one billion, six hundred thirty-six million, nine hundred seventy-one thousand, eight hundred fifty".