18661439221 has 2 divisors, whose sum is σ = 18661439222. Its totient is φ = 18661439220.

The previous prime is 18661439149. The next prime is 18661439233. The reversal of 18661439221 is 12293416681.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14706412900 + 3955026321 = 121270^2 + 62889^2 .

It is a cyclic number.

It is not a de Polignac number, because 18661439221 - 2⁹ = 18661438709 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18661439261) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9330719610 + 9330719611.

It is an arithmetic number, because the mean of its divisors is an integer number (9330719611).

Almost surely, 2^18661439221 is an apocalyptic number.

It is an amenable number.

18661439221 is a deficient number, since it is larger than the sum of its proper divisors (1).

18661439221 is an equidigital number, since it uses as much as digits as its factorization.

18661439221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 124416, while the sum is 43.

The spelling of 18661439221 in words is "eighteen billion, six hundred sixty-one million, four hundred thirty-nine thousand, two hundred twenty-one".