991263209 has 2 divisors, whose sum is σ = 991263210. Its totient is φ = 991263208.

The previous prime is 991263179. The next prime is 991263257. The reversal of 991263209 is 902362199.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 664195984 + 327067225 = 25772^2 + 18085^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-991263209 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (991223209) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495631604 + 495631605.

It is an arithmetic number, because the mean of its divisors is an integer number (495631605).

Almost surely, 2^991263209 is an apocalyptic number.

It is an amenable number.

991263209 is a deficient number, since it is larger than the sum of its proper divisors (1).

991263209 is an equidigital number, since it uses as much as digits as its factorization.

991263209 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 52488, while the sum is 41.

The square root of 991263209 is about 31484.3327545622. The cubic root of 991263209 is about 997.0792136461.

The spelling of 991263209 in words is "nine hundred ninety-one million, two hundred sixty-three thousand, two hundred nine".