638640640 has 80 divisors (see below), whose sum is σ = 1670518080. Its totient is φ = 232222720.

The previous prime is 638640623. The next prime is 638640647. The reversal of 638640640 is 46046836.

It is a tau number, because it is divible by the number of its divisors (80).

It is a self number, because there is not a number n which added to its sum of digits gives 638640640.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (638640647) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 16821 + ... + 39499.

It is an arithmetic number, because the mean of its divisors is an integer number (20881476).

Almost surely, 2^638640640 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 638640640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (835259040).

638640640 is an abundant number, since it is smaller than the sum of its proper divisors (1031877440).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

638640640 is a wasteful number, since it uses less digits than its factorization.

638640640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22713 (or 22697 counting only the distinct ones).

The product of its (nonzero) digits is 82944, while the sum is 37.

The square root of 638640640 is about 25271.3402889518. The cubic root of 638640640 is about 861.1633076219.

It can be divided in two parts, 638 and 640640, that added together give a triangular number (641278 = T₁₁₃₂).

The spelling of 638640640 in words is "six hundred thirty-eight million, six hundred forty thousand, six hundred forty".