16665581 has 2 divisors, whose sum is σ = 16665582. Its totient is φ = 16665580.

The previous prime is 16665563. The next prime is 16665599. The reversal of 16665581 is 18556661.

It is a balanced prime because it is at equal distance from previous prime (16665563) and next prime (16665599).

It can be written as a sum of positive squares in only one way, i.e., 16532356 + 133225 = 4066^2 + 365^2 .

It is a cyclic number.

It is not a de Polignac number, because 16665581 - 2¹⁴ = 16649197 is a prime.

It is a super-2 number, since 2×16665581² = 555483180135122, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (16665511) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8332790 + 8332791.

It is an arithmetic number, because the mean of its divisors is an integer number (8332791).

Almost surely, 2^16665581 is an apocalyptic number.

It is an amenable number.

16665581 is a deficient number, since it is larger than the sum of its proper divisors (1).

16665581 is an equidigital number, since it uses as much as digits as its factorization.

16665581 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 43200, while the sum is 38.

The square root of 16665581 is about 4082.3499360050. The cubic root of 16665581 is about 255.4309309667.

The spelling of 16665581 in words is "sixteen million, six hundred sixty-five thousand, five hundred eighty-one".