161581220 has 48 divisors (see below), whose sum is σ = 353801280. Its totient is φ = 61928064.

The previous prime is 161581177. The next prime is 161581223. The reversal of 161581220 is 22185161.

161581220 is digitally balanced in base 3, because in such base it contains all the possibile digits an equal number of times.

It is a super-2 number, since 2×161581220² = 52216981313376800, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 161581220.

It is not an unprimeable number, because it can be changed into a prime (161581223) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 47951 + ... + 51209.

It is an arithmetic number, because the mean of its divisors is an integer number (7370860).

Almost surely, 2^161581220 is an apocalyptic number.

161581220 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 161581220, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (176900640).

161581220 is an abundant number, since it is smaller than the sum of its proper divisors (192220060).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

161581220 is a wasteful number, since it uses less digits than its factorization.

161581220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3372 (or 3370 counting only the distinct ones).

The product of its (nonzero) digits is 960, while the sum is 26.

The square root of 161581220 is about 12711.4601836296. The cubic root of 161581220 is about 544.6660356110. Note that the first 3 decimals are identical.

The spelling of 161581220 in words is "one hundred sixty-one million, five hundred eighty-one thousand, two hundred twenty".