18205180921 has 2 divisors, whose sum is σ = 18205180922. Its totient is φ = 18205180920.

The previous prime is 18205180913. The next prime is 18205180927. The reversal of 18205180921 is 12908150281.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15921392400 + 2283788521 = 126180^2 + 47789^2 .

It is a cyclic number.

It is not a de Polignac number, because 18205180921 - 2³ = 18205180913 is a prime.

It is a super-2 number, since 2×18205180921² (a number of 21 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (18205180927) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9102590460 + 9102590461.

It is an arithmetic number, because the mean of its divisors is an integer number (9102590461).

Almost surely, 2^18205180921 is an apocalyptic number.

It is an amenable number.

18205180921 is a deficient number, since it is larger than the sum of its proper divisors (1).

18205180921 is an equidigital number, since it uses as much as digits as its factorization.

18205180921 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 11520, while the sum is 37.

The spelling of 18205180921 in words is "eighteen billion, two hundred five million, one hundred eighty thousand, nine hundred twenty-one".