81957789981 has 32 divisors (see below), whose sum is σ = 125652643200. Its totient is φ = 52734769920.

The previous prime is 81957789961. The next prime is 81957790003. The reversal of 81957789981 is 18998775918.

It is not a de Polignac number, because 81957789981 - 2⁹ = 81957789469 is a prime.

It is a super-2 number, since 2×81957789981² (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 (81957789961) 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, 2250286 + ... + 2286416.

It is an arithmetic number, because the mean of its divisors is an integer number (3926645100).

Almost surely, 2^81957789981 is an apocalyptic number.

It is an amenable number.

81957789981 is a deficient number, since it is larger than the sum of its proper divisors (43694853219).

81957789981 is a wasteful number, since it uses less digits than its factorization.

81957789981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 39066 (or 39060 counting only the distinct ones).

The product of its digits is 91445760, while the sum is 72.

The spelling of 81957789981 in words is "eighty-one billion, nine hundred fifty-seven million, seven hundred eighty-nine thousand, nine hundred eighty-one".