18155561 has 2 divisors, whose sum is σ = 18155562. Its totient is φ = 18155560.

The previous prime is 18155551. The next prime is 18155569. The reversal of 18155561 is 16555181.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18113536 + 42025 = 4256^2 + 205^2 .

It is an emirp because it is prime and its reverse (16555181) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18155561 - 2¹⁰ = 18154537 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (18155569) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9077780 + 9077781.

It is an arithmetic number, because the mean of its divisors is an integer number (9077781).

Almost surely, 2^18155561 is an apocalyptic number.

It is an amenable number.

18155561 is a deficient number, since it is larger than the sum of its proper divisors (1).

18155561 is an equidigital number, since it uses as much as digits as its factorization.

18155561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6000, while the sum is 32.

The square root of 18155561 is about 4260.9342872192. The cubic root of 18155561 is about 262.8269474131.

The spelling of 18155561 in words is "eighteen million, one hundred fifty-five thousand, five hundred sixty-one".