647601991 has 2 divisors, whose sum is σ = 647601992. Its totient is φ = 647601990.

The previous prime is 647601989. The next prime is 647602057. The reversal of 647601991 is 199106746.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 647601991 - 2¹ = 647601989 is a prime.

Together with 647601989, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (647601971) 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, 323800995 + 323800996.

It is an arithmetic number, because the mean of its divisors is an integer number (323800996).

Almost surely, 2^647601991 is an apocalyptic number.

647601991 is a deficient number, since it is larger than the sum of its proper divisors (1).

647601991 is an equidigital number, since it uses as much as digits as its factorization.

647601991 is an odious number, because the sum of its binary digits is odd.

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

The square root of 647601991 is about 25448.0252868469. The cubic root of 647601991 is about 865.1725366677.

The spelling of 647601991 in words is "six hundred forty-seven million, six hundred one thousand, nine hundred ninety-one".