166011561581 has 2 divisors, whose sum is σ = 166011561582. Its totient is φ = 166011561580.

The previous prime is 166011561539. The next prime is 166011561589. The reversal of 166011561581 is 185165110661.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 121462705225 + 44548856356 = 348515^2 + 211066^2 .

It is a cyclic number.

It is not a de Polignac number, because 166011561581 - 2¹⁰ = 166011560557 is a prime.

It is a super-2 number, since 2×166011561581² (a number of 23 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (166011561589) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 83005780790 + 83005780791.

It is an arithmetic number, because the mean of its divisors is an integer number (83005780791).

Almost surely, 2^166011561581 is an apocalyptic number.

It is an amenable number.

166011561581 is a deficient number, since it is larger than the sum of its proper divisors (1).

166011561581 is an equidigital number, since it uses as much as digits as its factorization.

166011561581 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 43200, while the sum is 41.

The spelling of 166011561581 in words is "one hundred sixty-six billion, eleven million, five hundred sixty-one thousand, five hundred eighty-one".