18981640 has 16 divisors (see below), whose sum is σ = 42708780. Its totient is φ = 7592640.

The previous prime is 18981617. The next prime is 18981649. The reversal of 18981640 is 4618981.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 16337764 + 2643876 = 4042^2 + 1626^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 18981640.

It is not an unprimeable number, because it can be changed into a prime (18981649) 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, 237231 + ... + 237310.

Almost surely, 2^18981640 is an apocalyptic number.

18981640 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

18981640 is an abundant number, since it is smaller than the sum of its proper divisors (23727140).

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

18981640 is a wasteful number, since it uses less digits than its factorization.

18981640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 474552 (or 474548 counting only the distinct ones).

The product of its (nonzero) digits is 13824, while the sum is 37.

The square root of 18981640 is about 4356.7923980837. The cubic root of 18981640 is about 266.7541865506.

The spelling of 18981640 in words is "eighteen million, nine hundred eighty-one thousand, six hundred forty".