81205977681 has 32 divisors (see below), whose sum is σ = 121589907840. Its totient is φ = 53560008000.

The previous prime is 81205977649. The next prime is 81205977691. The reversal of 81205977681 is 18677950218.

It is not a de Polignac number, because 81205977681 - 2⁵ = 81205977649 is a prime.

It is a super-2 number, since 2×81205977681² (a number of 23 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (81205977631) 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, 3755206 + ... + 3776768.

It is an arithmetic number, because the mean of its divisors is an integer number (3799684620).

Almost surely, 2^81205977681 is an apocalyptic number.

It is an amenable number.

81205977681 is a deficient number, since it is larger than the sum of its proper divisors (40383930159).

81205977681 is a wasteful number, since it uses less digits than its factorization.

81205977681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23054 (or 23048 counting only the distinct ones).

The product of its (nonzero) digits is 1693440, while the sum is 54.

The spelling of 81205977681 in words is "eighty-one billion, two hundred five million, nine hundred seventy-seven thousand, six hundred eighty-one".