166156721 has 2 divisors, whose sum is σ = 166156722. Its totient is φ = 166156720.

The previous prime is 166156699. The next prime is 166156763. The reversal of 166156721 is 127651661.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 107848225 + 58308496 = 10385^2 + 7636^2 .

It is an emirp because it is prime and its reverse (127651661) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 166156721 - 2¹⁰ = 166155697 is a prime.

It is not a weakly prime, because it can be changed into another prime (166156321) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 83078360 + 83078361.

It is an arithmetic number, because the mean of its divisors is an integer number (83078361).

Almost surely, 2^166156721 is an apocalyptic number.

It is an amenable number.

166156721 is a deficient number, since it is larger than the sum of its proper divisors (1).

166156721 is an equidigital number, since it uses as much as digits as its factorization.

166156721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 15120, while the sum is 35.

The square root of 166156721 is about 12890.1792462324. The cubic root of 166156721 is about 549.7593669111.

The spelling of 166156721 in words is "one hundred sixty-six million, one hundred fifty-six thousand, seven hundred twenty-one".