165807721 has 2 divisors, whose sum is σ = 165807722. Its totient is φ = 165807720.

The previous prime is 165807709. The next prime is 165807739. The reversal of 165807721 is 127708561.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 121771225 + 44036496 = 11035^2 + 6636^2 .

It is a cyclic number.

It is not a de Polignac number, because 165807721 - 2⁹ = 165807209 is a prime.

It is a Chen prime.

It is a nialpdrome in base 15.

It is not a weakly prime, because it can be changed into another prime (165807751) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 82903860 + 82903861.

It is an arithmetic number, because the mean of its divisors is an integer number (82903861).

Almost surely, 2^165807721 is an apocalyptic number.

It is an amenable number.

165807721 is a deficient number, since it is larger than the sum of its proper divisors (1).

165807721 is an equidigital number, since it uses as much as digits as its factorization.

165807721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 23520, while the sum is 37.

The square root of 165807721 is about 12876.6346923410. The cubic root of 165807721 is about 549.3741873683.

The spelling of 165807721 in words is "one hundred sixty-five million, eight hundred seven thousand, seven hundred twenty-one".