1638729444 has 72 divisors (see below), whose sum is σ = 4216482144. Its totient is φ = 491264000.

The previous prime is 1638729397. The next prime is 1638729457. The reversal of 1638729444 is 4449278361.

It is a junction number, because it is equal to n+sod(n) for n = 1638729393 and 1638729402.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1345924 + ... + 1347140.

It is an arithmetic number, because the mean of its divisors is an integer number (58562252).

Almost surely, 2^1638729444 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 1638729444, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2108241072).

1638729444 is an abundant number, since it is smaller than the sum of its proper divisors (2577752700).

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

1638729444 is a wasteful number, since it uses less digits than its factorization.

1638729444 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1437 (or 1334 counting only the distinct ones).

The product of its digits is 1161216, while the sum is 48.

The square root of 1638729444 is about 40481.2233510797. The cubic root of 1638729444 is about 1178.9690900294.

The spelling of 1638729444 in words is "one billion, six hundred thirty-eight million, seven hundred twenty-nine thousand, four hundred forty-four".