991358261 has 2 divisors, whose sum is σ = 991358262. Its totient is φ = 991358260.

The previous prime is 991358237. The next prime is 991358267. The reversal of 991358261 is 162853199.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 984014161 + 7344100 = 31369^2 + 2710^2 .

It is a cyclic number.

It is not a de Polignac number, because 991358261 - 2¹⁴ = 991341877 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991358267) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495679130 + 495679131.

It is an arithmetic number, because the mean of its divisors is an integer number (495679131).

Almost surely, 2^991358261 is an apocalyptic number.

It is an amenable number.

991358261 is a deficient number, since it is larger than the sum of its proper divisors (1).

991358261 is an equidigital number, since it uses as much as digits as its factorization.

991358261 is an evil number, because the sum of its binary digits is even.

The product of its digits is 116640, while the sum is 44.

The square root of 991358261 is about 31485.8422310727. The cubic root of 991358261 is about 997.1110825260. Note that the first 3 decimals are identical.

The spelling of 991358261 in words is "nine hundred ninety-one million, three hundred fifty-eight thousand, two hundred sixty-one".