991347557 has 2 divisors, whose sum is σ = 991347558. Its totient is φ = 991347556.

The previous prime is 991347551. The next prime is 991347589. The reversal of 991347557 is 755743199.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 884824516 + 106523041 = 29746^2 + 10321^2 .

It is a cyclic number.

It is not a de Polignac number, because 991347557 - 2⁶ = 991347493 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991347551) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495673778 + 495673779.

It is an arithmetic number, because the mean of its divisors is an integer number (495673779).

Almost surely, 2^991347557 is an apocalyptic number.

It is an amenable number.

991347557 is a deficient number, since it is larger than the sum of its proper divisors (1).

991347557 is an equidigital number, since it uses as much as digits as its factorization.

991347557 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1190700, while the sum is 50.

The square root of 991347557 is about 31485.6722494534. The cubic root of 991347557 is about 997.1074938081.

The spelling of 991347557 in words is "nine hundred ninety-one million, three hundred forty-seven thousand, five hundred fifty-seven".