81820188729 has 6 divisors (see below), whose sum is σ = 118184717066. Its totient is φ = 54546792480.

The previous prime is 81820188691. The next prime is 81820188731. The reversal of 81820188729 is 92788102818.

It can be written as a sum of positive squares in only one way, i.e., 62262725625 + 19557463104 = 249525^2 + 139848^2 .

It is not a de Polignac number, because 81820188729 - 2⁷ = 81820188601 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81820188929) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 4545566032 + ... + 4545566049.

Almost surely, 2^81820188729 is an apocalyptic number.

It is an amenable number.

81820188729 is a deficient number, since it is larger than the sum of its proper divisors (36364528337).

81820188729 is a wasteful number, since it uses less digits than its factorization.

81820188729 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9091132087 (or 9091132084 counting only the distinct ones).

The product of its (nonzero) digits is 1032192, while the sum is 54.

The spelling of 81820188729 in words is "eighty-one billion, eight hundred twenty million, one hundred eighty-eight thousand, seven hundred twenty-nine".