165987821 has 2 divisors, whose sum is σ = 165987822. Its totient is φ = 165987820.

The previous prime is 165987817. The next prime is 165987841. The reversal of 165987821 is 128789561.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 84897796 + 81090025 = 9214^2 + 9005^2 .

It is a cyclic number.

It is not a de Polignac number, because 165987821 - 2² = 165987817 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (165987841) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 82993910 + 82993911.

It is an arithmetic number, because the mean of its divisors is an integer number (82993911).

Almost surely, 2^165987821 is an apocalyptic number.

It is an amenable number.

165987821 is a deficient number, since it is larger than the sum of its proper divisors (1).

165987821 is an equidigital number, since it uses as much as digits as its factorization.

165987821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 241920, while the sum is 47.

The square root of 165987821 is about 12883.6260811931. The cubic root of 165987821 is about 549.5730250913.

The spelling of 165987821 in words is "one hundred sixty-five million, nine hundred eighty-seven thousand, eight hundred twenty-one".