18720209861 has 4 divisors (see below), whose sum is σ = 18720503712. Its totient is φ = 18719916012.

The previous prime is 18720209843. The next prime is 18720209881. The reversal of 18720209861 is 16890202781.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 16890202781 = 31 ⋅544845251.

It is a cyclic number.

It is not a de Polignac number, because 18720209861 - 2³⁴ = 1540340677 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18720209881) 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, 6851 + ... + 193616.

It is an arithmetic number, because the mean of its divisors is an integer number (4680125928).

Almost surely, 2^18720209861 is an apocalyptic number.

It is an amenable number.

18720209861 is a deficient number, since it is larger than the sum of its proper divisors (293851).

18720209861 is an equidigital number, since it uses as much as digits as its factorization.

18720209861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 293850.

The product of its (nonzero) digits is 96768, while the sum is 44.

It can be divided in two parts, 1872020 and 9861, that added together give a palindrome (1881881).

The spelling of 18720209861 in words is "eighteen billion, seven hundred twenty million, two hundred nine thousand, eight hundred sixty-one".