961991 has 2 divisors, whose sum is σ = 961992. Its totient is φ = 961990.

The previous prime is 961981. The next prime is 961993. The reversal of 961991 is 199169.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 961991 - 2⁶ = 961927 is a prime.

It is a Sophie Germain prime.

Together with 961993, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (961993) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 480995 + 480996.

It is an arithmetic number, because the mean of its divisors is an integer number (480996).

2⁹⁶¹⁹⁹¹ is an apocalyptic number.

961991 is a deficient number, since it is larger than the sum of its proper divisors (1).

961991 is an equidigital number, since it uses as much as digits as its factorization.

961991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4374, while the sum is 35.

The square root of 961991 is about 980.8113987918. The cubic root of 961991 is about 98.7166334956.

The spelling of 961991 in words is "nine hundred sixty-one thousand, nine hundred ninety-one".