12640643661 has 4 divisors (see below), whose sum is σ = 16854191552. Its totient is φ = 8427095772.

The previous prime is 12640643647. The next prime is 12640643681. The reversal of 12640643661 is 16634604621.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 12640643661 - 2⁹ = 12640643149 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (12640643681) 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, 2106773941 + ... + 2106773946.

It is an arithmetic number, because the mean of its divisors is an integer number (4213547888).

Almost surely, 2^12640643661 is an apocalyptic number.

It is an amenable number.

12640643661 is a deficient number, since it is larger than the sum of its proper divisors (4213547891).

12640643661 is an equidigital number, since it uses as much as digits as its factorization.

12640643661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4213547890.

The product of its (nonzero) digits is 124416, while the sum is 39.

The spelling of 12640643661 in words is "twelve billion, six hundred forty million, six hundred forty-three thousand, six hundred sixty-one".