18500561 has 2 divisors, whose sum is σ = 18500562. Its totient is φ = 18500560.

The previous prime is 18500557. The next prime is 18500567. The reversal of 18500561 is 16500581.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15840400 + 2660161 = 3980^2 + 1631^2 .

It is an emirp because it is prime and its reverse (16500581) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18500561 - 2² = 18500557 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 18500561.

It is not a weakly prime, because it can be changed into another prime (18500567) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9250280 + 9250281.

It is an arithmetic number, because the mean of its divisors is an integer number (9250281).

Almost surely, 2^18500561 is an apocalyptic number.

It is an amenable number.

18500561 is a deficient number, since it is larger than the sum of its proper divisors (1).

18500561 is an equidigital number, since it uses as much as digits as its factorization.

18500561 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1200, while the sum is 26.

The square root of 18500561 is about 4301.2278479523. The cubic root of 18500561 is about 264.4812969862.

The spelling of 18500561 in words is "eighteen million, five hundred thousand, five hundred sixty-one".