18821945561 has 2 divisors, whose sum is σ = 18821945562. Its totient is φ = 18821945560.

The previous prime is 18821945521. The next prime is 18821945599. The reversal of 18821945561 is 16554912881.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11078825536 + 7743120025 = 105256^2 + 87995^2 .

It is a cyclic number.

It is not a de Polignac number, because 18821945561 - 2⁶ = 18821945497 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (18821945521) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9410972780 + 9410972781.

It is an arithmetic number, because the mean of its divisors is an integer number (9410972781).

Almost surely, 2^18821945561 is an apocalyptic number.

It is an amenable number.

18821945561 is a deficient number, since it is larger than the sum of its proper divisors (1).

18821945561 is an equidigital number, since it uses as much as digits as its factorization.

18821945561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 691200, while the sum is 50.

The spelling of 18821945561 in words is "eighteen billion, eight hundred twenty-one million, nine hundred forty-five thousand, five hundred sixty-one".