891721077977 has 2 divisors, whose sum is σ = 891721077978. Its totient is φ = 891721077976.

The previous prime is 891721077943. The next prime is 891721078021. The reversal of 891721077977 is 779770127198.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 594280642816 + 297440435161 = 770896^2 + 545381^2 .

It is a cyclic number.

It is not a de Polignac number, because 891721077977 - 2⁸ = 891721077721 is a prime.

It is not a weakly prime, because it can be changed into another prime (891721077277) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 445860538988 + 445860538989.

It is an arithmetic number, because the mean of its divisors is an integer number (445860538989).

Almost surely, 2^891721077977 is an apocalyptic number.

It is an amenable number.

891721077977 is a deficient number, since it is larger than the sum of its proper divisors (1).

891721077977 is an equidigital number, since it uses as much as digits as its factorization.

891721077977 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 21781872, while the sum is 65.

The spelling of 891721077977 in words is "eight hundred ninety-one billion, seven hundred twenty-one million, seventy-seven thousand, nine hundred seventy-seven".