18563533721 has 2 divisors, whose sum is σ = 18563533722. Its totient is φ = 18563533720.

The previous prime is 18563533669. The next prime is 18563533733. The reversal of 18563533721 is 12733536581.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13674028096 + 4889505625 = 116936^2 + 69925^2 .

It is a cyclic number.

It is not a de Polignac number, because 18563533721 - 2¹⁴ = 18563517337 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 (18563533771) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9281766860 + 9281766861.

It is an arithmetic number, because the mean of its divisors is an integer number (9281766861).

Almost surely, 2^18563533721 is an apocalyptic number.

It is an amenable number.

18563533721 is a deficient number, since it is larger than the sum of its proper divisors (1).

18563533721 is an equidigital number, since it uses as much as digits as its factorization.

18563533721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 453600, while the sum is 44.

The spelling of 18563533721 in words is "eighteen billion, five hundred sixty-three million, five hundred thirty-three thousand, seven hundred twenty-one".