68640639 has 4 divisors (see below), whose sum is σ = 91520856. Its totient is φ = 45760424.

The previous prime is 68640631. The next prime is 68640647. The reversal of 68640639 is 93604686.

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

It is an interprime number because it is at equal distance from previous prime (68640631) and next prime (68640647).

It is a cyclic number.

It is not a de Polignac number, because 68640639 - 2³ = 68640631 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 68640639.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (68640631) 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, 11440104 + ... + 11440109.

It is an arithmetic number, because the mean of its divisors is an integer number (22880214).

Almost surely, 2^68640639 is an apocalyptic number.

68640639 is a deficient number, since it is larger than the sum of its proper divisors (22880217).

68640639 is a wasteful number, since it uses less digits than its factorization.

68640639 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22880216.

The product of its (nonzero) digits is 186624, while the sum is 42.

The square root of 68640639 is about 8284.9646348068. The cubic root of 68640639 is about 409.4433035536.

The spelling of 68640639 in words is "sixty-eight million, six hundred forty thousand, six hundred thirty-nine".