991297920061 has 2 divisors, whose sum is σ = 991297920062. Its totient is φ = 991297920060.

The previous prime is 991297920047. The next prime is 991297920077. The reversal of 991297920061 is 160029792199.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 585981064036 + 405316856025 = 765494^2 + 636645^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-991297920061 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 991297919984 and 991297920011.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991297920161) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495648960030 + 495648960031.

It is an arithmetic number, because the mean of its divisors is an integer number (495648960031).

Almost surely, 2^991297920061 is an apocalyptic number.

It is an amenable number.

991297920061 is a deficient number, since it is larger than the sum of its proper divisors (1).

991297920061 is an equidigital number, since it uses as much as digits as its factorization.

991297920061 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1102248, while the sum is 55.

The spelling of 991297920061 in words is "nine hundred ninety-one billion, two hundred ninety-seven million, nine hundred twenty thousand, sixty-one".