161221620 has 192 divisors, whose sum is σ = 539320320. Its totient is φ = 35223552.

The previous prime is 161221603. The next prime is 161221667. The reversal of 161221620 is 26122161.

161221620 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 1426684 + ... + 1426796.

It is an arithmetic number, because the mean of its divisors is an integer number (2808960).

Almost surely, 2^161221620 is an apocalyptic number.

161221620 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 161221620, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (269660160).

161221620 is an abundant number, since it is smaller than the sum of its proper divisors (378098700).

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

161221620 is a wasteful number, since it uses less digits than its factorization.

161221620 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 254 (or 252 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 21.

The square root of 161221620 is about 12697.3075886189. The cubic root of 161221620 is about 544.2616829608.

Adding to 161221620 its reverse (26122161), we get a palindrome (187343781).

It can be divided in two parts, 1612 and 21620, that added together give a palindrome (23232).

The spelling of 161221620 in words is "one hundred sixty-one million, two hundred twenty-one thousand, six hundred twenty".