18505561 has 2 divisors, whose sum is σ = 18505562. Its totient is φ = 18505560.

The previous prime is 18505541. The next prime is 18505579. The reversal of 18505561 is 16550581.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17799961 + 705600 = 4219^2 + 840^2 .

It is a cyclic number.

It is not a de Polignac number, because 18505561 - 2⁹ = 18505049 is a prime.

It is not a weakly prime, because it can be changed into another prime (18505541) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9252780 + 9252781.

It is an arithmetic number, because the mean of its divisors is an integer number (9252781).

Almost surely, 2^18505561 is an apocalyptic number.

It is an amenable number.

18505561 is a deficient number, since it is larger than the sum of its proper divisors (1).

18505561 is an equidigital number, since it uses as much as digits as its factorization.

18505561 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6000, while the sum is 31.

The square root of 18505561 is about 4301.8090380676. The cubic root of 18505561 is about 264.5051212614.

The spelling of 18505561 in words is "eighteen million, five hundred five thousand, five hundred sixty-one".