81563928977 has 2 divisors, whose sum is σ = 81563928978. Its totient is φ = 81563928976.

The previous prime is 81563928913. The next prime is 81563928991. The reversal of 81563928977 is 77982936518.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 80406840721 + 1157088256 = 283561^2 + 34016^2 .

It is a cyclic number.

It is not a de Polignac number, because 81563928977 - 2⁶ = 81563928913 is a prime.

It is not a weakly prime, because it can be changed into another prime (81563928577) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40781964488 + 40781964489.

It is an arithmetic number, because the mean of its divisors is an integer number (40781964489).

Almost surely, 2^81563928977 is an apocalyptic number.

It is an amenable number.

81563928977 is a deficient number, since it is larger than the sum of its proper divisors (1).

81563928977 is an equidigital number, since it uses as much as digits as its factorization.

81563928977 is an evil number, because the sum of its binary digits is even.

The product of its digits is 45722880, while the sum is 65.

The spelling of 81563928977 in words is "eighty-one billion, five hundred sixty-three million, nine hundred twenty-eight thousand, nine hundred seventy-seven".