18378821 has 2 divisors, whose sum is σ = 18378822. Its totient is φ = 18378820.

The previous prime is 18378803. The next prime is 18378823. The reversal of 18378821 is 12887381.

18378821 is nontrivially palindromic in base 5.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18369796 + 9025 = 4286^2 + 95^2 .

It is a cyclic number.

It is not a de Polignac number, because 18378821 - 2¹⁰ = 18377797 is a prime.

It is a super-2 number, since 2×18378821² = 675562122700082, which contains 22 as substring.

Together with 18378823, 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 (18378823) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9189410 + 9189411.

It is an arithmetic number, because the mean of its divisors is an integer number (9189411).

Almost surely, 2^18378821 is an apocalyptic number.

It is an amenable number.

18378821 is a deficient number, since it is larger than the sum of its proper divisors (1).

18378821 is an equidigital number, since it uses as much as digits as its factorization.

18378821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 21504, while the sum is 38.

The square root of 18378821 is about 4287.0527171939. The cubic root of 18378821 is about 263.8998941318.

The spelling of 18378821 in words is "eighteen million, three hundred seventy-eight thousand, eight hundred twenty-one".