166451821 has 2 divisors, whose sum is σ = 166451822. Its totient is φ = 166451820.

The previous prime is 166451819. The next prime is 166451843. The reversal of 166451821 is 128154661.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 142539721 + 23912100 = 11939^2 + 4890^2 .

It is an emirp because it is prime and its reverse (128154661) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 166451821 - 2¹ = 166451819 is a prime.

Together with 166451819, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (166452821) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 83225910 + 83225911.

It is an arithmetic number, because the mean of its divisors is an integer number (83225911).

Almost surely, 2^166451821 is an apocalyptic number.

It is an amenable number.

166451821 is a deficient number, since it is larger than the sum of its proper divisors (1).

166451821 is an equidigital number, since it uses as much as digits as its factorization.

166451821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 11520, while the sum is 34.

The square root of 166451821 is about 12901.6208671624. The cubic root of 166451821 is about 550.0846382142.

The spelling of 166451821 in words is "one hundred sixty-six million, four hundred fifty-one thousand, eight hundred twenty-one".