81977894857 has 2 divisors, whose sum is σ = 81977894858. Its totient is φ = 81977894856.

The previous prime is 81977894837. The next prime is 81977894899. The reversal of 81977894857 is 75849877918.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 42245047296 + 39732847561 = 205536^2 + 199331^2 .

It is a cyclic number.

It is not a de Polignac number, because 81977894857 - 2⁷ = 81977894729 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 81977894857.

It is not a weakly prime, because it can be changed into another prime (81977894807) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40988947428 + 40988947429.

It is an arithmetic number, because the mean of its divisors is an integer number (40988947429).

Almost surely, 2^81977894857 is an apocalyptic number.

It is an amenable number.

81977894857 is a deficient number, since it is larger than the sum of its proper divisors (1).

81977894857 is an equidigital number, since it uses as much as digits as its factorization.

81977894857 is an evil number, because the sum of its binary digits is even.

The product of its digits is 284497920, while the sum is 73.

The spelling of 81977894857 in words is "eighty-one billion, nine hundred seventy-seven million, eight hundred ninety-four thousand, eight hundred fifty-seven".