166537781 has 2 divisors, whose sum is σ = 166537782. Its totient is φ = 166537780.

The previous prime is 166537771. The next prime is 166537783. The reversal of 166537781 is 187735661.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 135512881 + 31024900 = 11641^2 + 5570^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-166537781 is a prime.

It is a super-2 number, since 2×166537781² = 55469665000807922, which contains 22 as substring.

Together with 166537783, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (166537783) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 83268890 + 83268891.

It is an arithmetic number, because the mean of its divisors is an integer number (83268891).

Almost surely, 2^166537781 is an apocalyptic number.

It is an amenable number.

166537781 is a deficient number, since it is larger than the sum of its proper divisors (1).

166537781 is an equidigital number, since it uses as much as digits as its factorization.

166537781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 211680, while the sum is 44.

The square root of 166537781 is about 12904.9518015373. The cubic root of 166537781 is about 550.1793145351.

The spelling of 166537781 in words is "one hundred sixty-six million, five hundred thirty-seven thousand, seven hundred eighty-one".