18408423821 has 2 divisors, whose sum is σ = 18408423822. Its totient is φ = 18408423820.

The previous prime is 18408423791. The next prime is 18408423823. The reversal of 18408423821 is 12832480481.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12086583721 + 6321840100 = 109939^2 + 79510^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18408423821 is a prime.

Together with 18408423823, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18408423823) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9204211910 + 9204211911.

It is an arithmetic number, because the mean of its divisors is an integer number (9204211911).

Almost surely, 2^18408423821 is an apocalyptic number.

It is an amenable number.

18408423821 is a deficient number, since it is larger than the sum of its proper divisors (1).

18408423821 is an equidigital number, since it uses as much as digits as its factorization.

18408423821 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 98304, while the sum is 41.

The spelling of 18408423821 in words is "eighteen billion, four hundred eight million, four hundred twenty-three thousand, eight hundred twenty-one".