81999999999997 has 2 divisors, whose sum is σ = 81999999999998. Its totient is φ = 81999999999996.

The previous prime is 81999999999949. The next prime is 82000000000003. The reversal of 81999999999997 is 79999999999918.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 80633593303641 + 1366406696356 = 8979621^2 + 1168934^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81999999999997 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81999999993997) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40999999999998 + 40999999999999.

It is an arithmetic number, because the mean of its divisors is an integer number (40999999999999).

Almost surely, 2^{81999999999997} is an apocalyptic number.

It is an amenable number.

81999999999997 is a deficient number, since it is larger than the sum of its proper divisors (1).

81999999999997 is an equidigital number, since it uses as much as digits as its factorization.

81999999999997 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1757339338104, while the sum is 115.

The spelling of 81999999999997 in words is "eighty-one trillion, nine hundred ninety-nine billion, nine hundred ninety-nine million, nine hundred ninety-nine thousand, nine hundred ninety-seven".