991581077 has 2 divisors, whose sum is σ = 991581078. Its totient is φ = 991581076.

The previous prime is 991581067. The next prime is 991581089. The reversal of 991581077 is 770185199.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 750431236 + 241149841 = 27394^2 + 15529^2 .

It is a cyclic number.

It is not a de Polignac number, because 991581077 - 2¹⁰ = 991580053 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991581067) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495790538 + 495790539.

It is an arithmetic number, because the mean of its divisors is an integer number (495790539).

Almost surely, 2^991581077 is an apocalyptic number.

It is an amenable number.

991581077 is a deficient number, since it is larger than the sum of its proper divisors (1).

991581077 is an equidigital number, since it uses as much as digits as its factorization.

991581077 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 158760, while the sum is 47.

The square root of 991581077 is about 31489.3803845042. The cubic root of 991581077 is about 997.1857799281.

The spelling of 991581077 in words is "nine hundred ninety-one million, five hundred eighty-one thousand, seventy-seven".