991237813 has 2 divisors, whose sum is σ = 991237814. Its totient is φ = 991237812.

The previous prime is 991237811. The next prime is 991237817. The reversal of 991237813 is 318732199.

991237813 = 22262² + 22263².

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 495641169 + 495596644 = 22263^2 + 22262^2 .

It is a cyclic number.

It is not a de Polignac number, because 991237813 - 2¹ = 991237811 is a prime.

Together with 991237811, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 991237813.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991237811) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495618906 + 495618907.

It is an arithmetic number, because the mean of its divisors is an integer number (495618907).

Almost surely, 2^991237813 is an apocalyptic number.

991237813 is the 22263-rd centered square number.

It is an amenable number.

991237813 is a deficient number, since it is larger than the sum of its proper divisors (1).

991237813 is an equidigital number, since it uses as much as digits as its factorization.

991237813 is an evil number, because the sum of its binary digits is even.

The product of its digits is 81648, while the sum is 43.

The square root of 991237813 is about 31483.9294402716. The cubic root of 991237813 is about 997.0706985717.

The spelling of 991237813 in words is "nine hundred ninety-one million, two hundred thirty-seven thousand, eight hundred thirteen".