18947291821 has 2 divisors, whose sum is σ = 18947291822. Its totient is φ = 18947291820.

The previous prime is 18947291813. The next prime is 18947291827. The reversal of 18947291821 is 12819274981.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11281413796 + 7665878025 = 106214^2 + 87555^2 .

It is a cyclic number.

It is not a de Polignac number, because 18947291821 - 2³ = 18947291813 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18947291827) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9473645910 + 9473645911.

It is an arithmetic number, because the mean of its divisors is an integer number (9473645911).

Almost surely, 2^18947291821 is an apocalyptic number.

It is an amenable number.

18947291821 is a deficient number, since it is larger than the sum of its proper divisors (1).

18947291821 is an equidigital number, since it uses as much as digits as its factorization.

18947291821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 580608, while the sum is 52.

The spelling of 18947291821 in words is "eighteen billion, nine hundred forty-seven million, two hundred ninety-one thousand, eight hundred twenty-one".