16561999940 has 24 divisors (see below), whose sum is σ = 35720206872. Its totient is φ = 6445751040.

The previous prime is 16561999939. The next prime is 16561999997. The reversal of 16561999940 is 4999916561.

It can be written as a sum of positive squares in 4 ways, for example, as 7050289156 + 9511710784 = 83966^2 + 97528^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 16561999940.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 11189801 + ... + 11191280.

It is an arithmetic number, because the mean of its divisors is an integer number (1488341953).

Almost surely, 2^16561999940 is an apocalyptic number.

16561999940 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

16561999940 is an abundant number, since it is smaller than the sum of its proper divisors (19158206932).

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

16561999940 is a wasteful number, since it uses less digits than its factorization.

16561999940 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22381127 (or 22381125 counting only the distinct ones).

The product of its (nonzero) digits is 4723920, while the sum is 59.

The spelling of 16561999940 in words is "sixteen billion, five hundred sixty-one million, nine hundred ninety-nine thousand, nine hundred forty".