161221800 has 96 divisors (see below), whose sum is σ = 503092800. Its totient is φ = 42708480.

The previous prime is 161221771. The next prime is 161221843. The reversal of 161221800 is 8122161.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 99396 + ... + 101004.

It is an arithmetic number, because the mean of its divisors is an integer number (5240550).

Almost surely, 2^161221800 is an apocalyptic number.

161221800 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 161221800, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (251546400).

161221800 is an abundant number, since it is smaller than the sum of its proper divisors (341871000).

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

161221800 is a wasteful number, since it uses less digits than its factorization.

161221800 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1795 (or 1786 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 21.

The square root of 161221800 is about 12697.3146767338. The cubic root of 161221800 is about 544.2618855123.

Adding to 161221800 its reverse (8122161), we get a palindrome (169343961).

The spelling of 161221800 in words is "one hundred sixty-one million, two hundred twenty-one thousand, eight hundred".