691243991 has 2 divisors, whose sum is σ = 691243992. Its totient is φ = 691243990.

The previous prime is 691243981. The next prime is 691243999. The reversal of 691243991 is 199342196.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-691243991 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (691243999) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 345621995 + 345621996.

It is an arithmetic number, because the mean of its divisors is an integer number (345621996).

Almost surely, 2^691243991 is an apocalyptic number.

691243991 is a deficient number, since it is larger than the sum of its proper divisors (1).

691243991 is an equidigital number, since it uses as much as digits as its factorization.

691243991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 104976, while the sum is 44.

The square root of 691243991 is about 26291.5193741252. The cubic root of 691243991 is about 884.1863167098.

The spelling of 691243991 in words is "six hundred ninety-one million, two hundred forty-three thousand, nine hundred ninety-one".