166221561 has 8 divisors (see below), whose sum is σ = 241776864. Its totient is φ = 100740320.

The previous prime is 166221553. The next prime is 166221589. The reversal of 166221561 is 165122661.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 166221561 - 2³ = 166221553 is a prime.

It is not an unprimeable number, because it can be changed into a prime (166221521) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2518476 + ... + 2518541.

It is an arithmetic number, because the mean of its divisors is an integer number (30222108).

Almost surely, 2^166221561 is an apocalyptic number.

166221561 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

166221561 is a deficient number, since it is larger than the sum of its proper divisors (75555303).

166221561 is a wasteful number, since it uses less digits than its factorization.

166221561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5037031.

The product of its digits is 4320, while the sum is 30.

The square root of 166221561 is about 12892.6940939433. The cubic root of 166221561 is about 549.8308692080.

The spelling of 166221561 in words is "one hundred sixty-six million, two hundred twenty-one thousand, five hundred sixty-one".