81121996820 has 96 divisors (see below), whose sum is σ = 188242790400. Its totient is φ = 29227803264.

The previous prime is 81121996819. The next prime is 81121996829. The reversal of 81121996820 is 2869912118.

It is a super-2 number, since 2×81121996820² (a number of 23 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81121996829) 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, 1431791 + ... + 1487369.

It is an arithmetic number, because the mean of its divisors is an integer number (1960862400).

Almost surely, 2^81121996820 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 81121996820, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (94121395200).

81121996820 is an abundant number, since it is smaller than the sum of its proper divisors (107120793580).

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

81121996820 is a wasteful number, since it uses less digits than its factorization.

81121996820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 55797 (or 55795 counting only the distinct ones).

The product of its (nonzero) digits is 124416, while the sum is 47.

The spelling of 81121996820 in words is "eighty-one billion, one hundred twenty-one million, nine hundred ninety-six thousand, eight hundred twenty".