647661391 has 4 divisors (see below), whose sum is σ = 697481512. Its totient is φ = 597841272.

The previous prime is 647661373. The next prime is 647661403. The reversal of 647661391 is 193166746.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 647661391 - 2⁹ = 647660879 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (647665391) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 24910041 + ... + 24910066.

It is an arithmetic number, because the mean of its divisors is an integer number (174370378).

Almost surely, 2^647661391 is an apocalyptic number.

647661391 is a deficient number, since it is larger than the sum of its proper divisors (49820121).

647661391 is a wasteful number, since it uses less digits than its factorization.

647661391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 49820120.

The product of its digits is 163296, while the sum is 43.

The square root of 647661391 is about 25449.1923447484. The cubic root of 647661391 is about 865.1989879337.

The spelling of 647661391 in words is "six hundred forty-seven million, six hundred sixty-one thousand, three hundred ninety-one".