165851821 has 2 divisors, whose sum is σ = 165851822. Its totient is φ = 165851820.

The previous prime is 165851759. The next prime is 165851831. The reversal of 165851821 is 128158561.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 130210921 + 35640900 = 11411^2 + 5970^2 .

It is a cyclic number.

It is not a de Polignac number, because 165851821 - 2²³ = 157463213 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (165851831) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 82925910 + 82925911.

It is an arithmetic number, because the mean of its divisors is an integer number (82925911).

Almost surely, 2^165851821 is an apocalyptic number.

It is an amenable number.

165851821 is a deficient number, since it is larger than the sum of its proper divisors (1).

165851821 is an equidigital number, since it uses as much as digits as its factorization.

165851821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 19200, while the sum is 37.

The square root of 165851821 is about 12878.3469824353. The cubic root of 165851821 is about 549.4228888680.

The spelling of 165851821 in words is "one hundred sixty-five million, eight hundred fifty-one thousand, eight hundred twenty-one".