18321551 has 2 divisors, whose sum is σ = 18321552. Its totient is φ = 18321550.

The previous prime is 18321539. The next prime is 18321553. The reversal of 18321551 is 15512381.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18321551 is a prime.

Together with 18321553, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 18321551.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18321553) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9160775 + 9160776.

It is an arithmetic number, because the mean of its divisors is an integer number (9160776).

Almost surely, 2^18321551 is an apocalyptic number.

18321551 is a deficient number, since it is larger than the sum of its proper divisors (1).

18321551 is an equidigital number, since it uses as much as digits as its factorization.

18321551 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1200, while the sum is 26.

The square root of 18321551 is about 4280.3680916482. The cubic root of 18321551 is about 263.6254972677.

The spelling of 18321551 in words is "eighteen million, three hundred twenty-one thousand, five hundred fifty-one".