991951 has 2 divisors, whose sum is σ = 991952. Its totient is φ = 991950.

The previous prime is 991943. The next prime is 991957. The reversal of 991951 is 159199.

It is a strong prime.

It is an emirp because it is prime and its reverse (159199) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 991951 - 2³ = 991943 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991957) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495975 + 495976.

It is an arithmetic number, because the mean of its divisors is an integer number (495976).

2⁹⁹¹⁹⁵¹ is an apocalyptic number.

991951 is a deficient number, since it is larger than the sum of its proper divisors (1).

991951 is an equidigital number, since it uses as much as digits as its factorization.

991951 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3645, while the sum is 34.

The square root of 991951 is about 995.9673689434. The cubic root of 991951 is about 99.7309769148.

The spelling of 991951 in words is "nine hundred ninety-one thousand, nine hundred fifty-one".