18281621 has 2 divisors, whose sum is σ = 18281622. Its totient is φ = 18281620.

The previous prime is 18281603. The next prime is 18281633. The reversal of 18281621 is 12618281.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15689521 + 2592100 = 3961^2 + 1610^2 .

It is a cyclic number.

It is not a de Polignac number, because 18281621 - 2¹⁰ = 18280597 is a prime.

It is a Chen prime.

It is equal to p_1168166 and since 18281621 and 1168166 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18281651) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9140810 + 9140811.

It is an arithmetic number, because the mean of its divisors is an integer number (9140811).

Almost surely, 2^18281621 is an apocalyptic number.

It is an amenable number.

18281621 is a deficient number, since it is larger than the sum of its proper divisors (1).

18281621 is an equidigital number, since it uses as much as digits as its factorization.

18281621 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1536, while the sum is 29.

The square root of 18281621 is about 4275.7012290383. The cubic root of 18281621 is about 263.4338427769.

The spelling of 18281621 in words is "eighteen million, two hundred eighty-one thousand, six hundred twenty-one".