18187208721 has 40 divisors (see below), whose sum is σ = 29657320704. Its totient is φ = 11015520480.

The previous prime is 18187208653. The next prime is 18187208723. The reversal of 18187208721 is 12780278181.

It is a happy number.

It is not a de Polignac number, because 18187208721 - 2⁷ = 18187208593 is a prime.

It is a super-2 number, since 2×18187208721² (a number of 21 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (18187208723) by changing a digit.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 1618695 + ... + 1629891.

Almost surely, 2^18187208721 is an apocalyptic number.

18187208721 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

18187208721 is a deficient number, since it is larger than the sum of its proper divisors (11470111983).

18187208721 is a wasteful number, since it uses less digits than its factorization.

18187208721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13043 (or 13034 counting only the distinct ones).

The product of its (nonzero) digits is 100352, while the sum is 45.

The spelling of 18187208721 in words is "eighteen billion, one hundred eighty-seven million, two hundred eight thousand, seven hundred twenty-one".