18645581 has 2 divisors, whose sum is σ = 18645582. Its totient is φ = 18645580.

The previous prime is 18645577. The next prime is 18645619. The reversal of 18645581 is 18554681.

It is an a-pointer prime, because the next prime (18645619) can be obtained adding 18645581 to its sum of digits (38).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12716356 + 5929225 = 3566^2 + 2435^2 .

It is an emirp because it is prime and its reverse (18554681) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18645581 - 2² = 18645577 is a prime.

It is a super-2 number, since 2×18645581² = 695315381655122, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18645541) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9322790 + 9322791.

It is an arithmetic number, because the mean of its divisors is an integer number (9322791).

Almost surely, 2^18645581 is an apocalyptic number.

It is an amenable number.

18645581 is a deficient number, since it is larger than the sum of its proper divisors (1).

18645581 is an equidigital number, since it uses as much as digits as its factorization.

18645581 is an evil number, because the sum of its binary digits is even.

The product of its digits is 38400, while the sum is 38.

The square root of 18645581 is about 4318.0529176933. The cubic root of 18645581 is about 265.1705606633.

The spelling of 18645581 in words is "eighteen million, six hundred forty-five thousand, five hundred eighty-one".