18918421 has 2 divisors, whose sum is σ = 18918422. Its totient is φ = 18918420.

The previous prime is 18918413. The next prime is 18918437. The reversal of 18918421 is 12481981.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11655396 + 7263025 = 3414^2 + 2695^2 .

It is a cyclic number.

It is not a de Polignac number, because 18918421 - 2³ = 18918413 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18918451) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9459210 + 9459211.

It is an arithmetic number, because the mean of its divisors is an integer number (9459211).

Almost surely, 2^18918421 is an apocalyptic number.

It is an amenable number.

18918421 is a deficient number, since it is larger than the sum of its proper divisors (1).

18918421 is an equidigital number, since it uses as much as digits as its factorization.

18918421 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4608, while the sum is 34.

The square root of 18918421 is about 4349.5311241558. The cubic root of 18918421 is about 266.4577125262.

The spelling of 18918421 in words is "eighteen million, nine hundred eighteen thousand, four hundred twenty-one".