18355621 has 2 divisors, whose sum is σ = 18355622. Its totient is φ = 18355620.

The previous prime is 18355613. The next prime is 18355657. The reversal of 18355621 is 12655381.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11464996 + 6890625 = 3386^2 + 2625^2 .

It is an emirp because it is prime and its reverse (12655381) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18355621 - 2³ = 18355613 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18355021) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9177810 + 9177811.

It is an arithmetic number, because the mean of its divisors is an integer number (9177811).

Almost surely, 2^18355621 is an apocalyptic number.

It is an amenable number.

18355621 is a deficient number, since it is larger than the sum of its proper divisors (1).

18355621 is an equidigital number, since it uses as much as digits as its factorization.

18355621 is an evil number, because the sum of its binary digits is even.

The product of its digits is 7200, while the sum is 31.

The square root of 18355621 is about 4284.3460411129. The cubic root of 18355621 is about 263.7888051137.

The spelling of 18355621 in words is "eighteen million, three hundred fifty-five thousand, six hundred twenty-one".