81339531857 has 2 divisors, whose sum is σ = 81339531858. Its totient is φ = 81339531856.

The previous prime is 81339531853. The next prime is 81339531893. The reversal of 81339531857 is 75813593318.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 43414306321 + 37925225536 = 208361^2 + 194744^2 .

It is a cyclic number.

It is not a de Polignac number, because 81339531857 - 2² = 81339531853 is a prime.

It is a super-2 number, since 2×81339531857² (a number of 23 digits) contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 81339531799 and 81339531808.

It is not a weakly prime, because it can be changed into another prime (81339531853) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40669765928 + 40669765929.

It is an arithmetic number, because the mean of its divisors is an integer number (40669765929).

Almost surely, 2^81339531857 is an apocalyptic number.

It is an amenable number.

81339531857 is a deficient number, since it is larger than the sum of its proper divisors (1).

81339531857 is an equidigital number, since it uses as much as digits as its factorization.

81339531857 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2721600, while the sum is 53.

The spelling of 81339531857 in words is "eighty-one billion, three hundred thirty-nine million, five hundred thirty-one thousand, eight hundred fifty-seven".