18197121561 has 4 divisors (see below), whose sum is σ = 24262828752. Its totient is φ = 12131414372.

The previous prime is 18197121559. The next prime is 18197121571. The reversal of 18197121561 is 16512179181.

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.

It is a cyclic number.

It is not a de Polignac number, because 18197121561 - 2¹ = 18197121559 is a prime.

It is a super-2 number, since 2×18197121561² (a number of 21 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (18197121511) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3032853591 + ... + 3032853596.

It is an arithmetic number, because the mean of its divisors is an integer number (6065707188).

Almost surely, 2^18197121561 is an apocalyptic number.

It is an amenable number.

18197121561 is a deficient number, since it is larger than the sum of its proper divisors (6065707191).

18197121561 is an equidigital number, since it uses as much as digits as its factorization.

18197121561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6065707190.

The product of its digits is 30240, while the sum is 42.

The spelling of 18197121561 in words is "eighteen billion, one hundred ninety-seven million, one hundred twenty-one thousand, five hundred sixty-one".