161821836 has 144 divisors (see below), whose sum is σ = 472792320. Its totient is φ = 46189440.

The previous prime is 161821823. The next prime is 161821853. The reversal of 161821836 is 638128161.

161821836 is a `hidden beast` number, since 1 + 618 + 2 + 1 + 8 + 36 = 666.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a self number, because there is not a number n which added to its sum of digits gives 161821836.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 992691 + ... + 992853.

It is an arithmetic number, because the mean of its divisors is an integer number (3283280).

Almost surely, 2^161821836 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 161821836, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (236396160).

161821836 is an abundant number, since it is smaller than the sum of its proper divisors (310970484).

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

161821836 is a wasteful number, since it uses less digits than its factorization.

161821836 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 316 (or 311 counting only the distinct ones).

The product of its digits is 13824, while the sum is 36.

The square root of 161821836 is about 12720.9211930583. The cubic root of 161821836 is about 544.9362616592.

Adding to 161821836 its reverse (638128161), we get a palindrome (799949997).

The spelling of 161821836 in words is "one hundred sixty-one million, eight hundred twenty-one thousand, eight hundred thirty-six".