19981638 has 48 divisors (see below), whose sum is σ = 45349200. Its totient is φ = 6350400.

The previous prime is 19981567. The next prime is 19981649. The reversal of 19981638 is 83618991.

19981638 is a `hidden beast` number, since 1 + 9 + 9 + 8 + 1 + 638 = 666.

It is a junction number, because it is equal to n+sod(n) for n = 19981593 and 19981602.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 52533 + ... + 52911.

It is an arithmetic number, because the mean of its divisors is an integer number (944775).

Almost surely, 2^19981638 is an apocalyptic number.

19981638 is a gapful number since it is divisible by the number (18) formed by its first and last digit.

It is a practical number, because each smaller number is the sum of distinct divisors of 19981638, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22674600).

19981638 is an abundant number, since it is smaller than the sum of its proper divisors (25367562).

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

19981638 is a wasteful number, since it uses less digits than its factorization.

19981638 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 517 (or 514 counting only the distinct ones).

The product of its digits is 93312, while the sum is 45.

The square root of 19981638 is about 4470.0825495733. The cubic root of 19981638 is about 271.3586659971.

The spelling of 19981638 in words is "nineteen million, nine hundred eighty-one thousand, six hundred thirty-eight".