647991 has 6 divisors (see below), whose sum is σ = 936000. Its totient is φ = 431988.

The previous prime is 647987. The next prime is 648007. The reversal of 647991 is 199746.

647991 is a `hidden beast` number, since 647 + 9 + 9 + 1 = 666.

It is not a de Polignac number, because 647991 - 2² = 647987 is a prime.

647991 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (647951) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 35991 + ... + 36008.

It is an arithmetic number, because the mean of its divisors is an integer number (156000).

2⁶⁴⁷⁹⁹¹ is an apocalyptic number.

647991 is a deficient number, since it is larger than the sum of its proper divisors (288009).

647991 is a wasteful number, since it uses less digits than its factorization.

647991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 72005 (or 72002 counting only the distinct ones).

The product of its digits is 13608, while the sum is 36.

The square root of 647991 is about 804.9788817106. The cubic root of 647991 is about 86.5345735917.

The spelling of 647991 in words is "six hundred forty-seven thousand, nine hundred ninety-one".