21205618193 has 2 divisors, whose sum is σ = 21205618194. Its totient is φ = 21205618192.

The previous prime is 21205618153. The next prime is 21205618207. The reversal of 21205618193 is 39181650212.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21098143504 + 107474689 = 145252^2 + 10367^2 .

It is a cyclic number.

It is not a de Polignac number, because 21205618193 - 2²⁴ = 21188840977 is a prime.

It is not a weakly prime, because it can be changed into another prime (21205618153) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10602809096 + 10602809097.

It is an arithmetic number, because the mean of its divisors is an integer number (10602809097).

Almost surely, 2^21205618193 is an apocalyptic number.

It is an amenable number.

21205618193 is a deficient number, since it is larger than the sum of its proper divisors (1).

21205618193 is an equidigital number, since it uses as much as digits as its factorization.

21205618193 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 25920, while the sum is 38.

The spelling of 21205618193 in words is "twenty-one billion, two hundred five million, six hundred eighteen thousand, one hundred ninety-three".