661643647 has 4 divisors (see below), whose sum is σ = 756164176. Its totient is φ = 567123120.

The previous prime is 661643629. The next prime is 661643659. The reversal of 661643647 is 746346166.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-661643647 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661643677) 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, 47260254 + ... + 47260267.

It is an arithmetic number, because the mean of its divisors is an integer number (189041044).

Almost surely, 2^661643647 is an apocalyptic number.

661643647 is a deficient number, since it is larger than the sum of its proper divisors (94520529).

661643647 is an equidigital number, since it uses as much as digits as its factorization.

661643647 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 94520528.

The product of its digits is 435456, while the sum is 43.

The square root of 661643647 is about 25722.4347020262. The cubic root of 661643647 is about 871.3809253598.

The spelling of 661643647 in words is "six hundred sixty-one million, six hundred forty-three thousand, six hundred forty-seven".