18640561 has 2 divisors, whose sum is σ = 18640562. Its totient is φ = 18640560.

The previous prime is 18640549. The next prime is 18640621. The reversal of 18640561 is 16504681.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18326961 + 313600 = 4281^2 + 560^2 .

It is an emirp because it is prime and its reverse (16504681) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18640561 - 2²³ = 10251953 is a prime.

It is not a weakly prime, because it can be changed into another prime (18640541) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9320280 + 9320281.

It is an arithmetic number, because the mean of its divisors is an integer number (9320281).

Almost surely, 2^18640561 is an apocalyptic number.

It is an amenable number.

18640561 is a deficient number, since it is larger than the sum of its proper divisors (1).

18640561 is an equidigital number, since it uses as much as digits as its factorization.

18640561 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 5760, while the sum is 31.

The square root of 18640561 is about 4317.4715980537. The cubic root of 18640561 is about 265.1467609992.

The spelling of 18640561 in words is "eighteen million, six hundred forty thousand, five hundred sixty-one".