991291001977 has 2 divisors, whose sum is σ = 991291001978. Its totient is φ = 991291001976.

The previous prime is 991291001969. The next prime is 991291002043. The reversal of 991291001977 is 779100192199.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 754841241856 + 236449760121 = 868816^2 + 486261^2 .

It is a cyclic number.

It is not a de Polignac number, because 991291001977 - 2³ = 991291001969 is a prime.

It is not a weakly prime, because it can be changed into another prime (991291001377) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495645500988 + 495645500989.

It is an arithmetic number, because the mean of its divisors is an integer number (495645500989).

Almost surely, 2^991291001977 is an apocalyptic number.

It is an amenable number.

991291001977 is a deficient number, since it is larger than the sum of its proper divisors (1).

991291001977 is an equidigital number, since it uses as much as digits as its factorization.

991291001977 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 642978, while the sum is 55.

The spelling of 991291001977 in words is "nine hundred ninety-one billion, two hundred ninety-one million, one thousand, nine hundred seventy-seven".