161989821 has 32 divisors (see below), whose sum is σ = 290407680. Its totient is φ = 87118848.

The previous prime is 161989819. The next prime is 161989823. The reversal of 161989821 is 128989161.

161989821 is a `hidden beast` number, since 1 + 619 + 8 + 9 + 8 + 21 = 666.

It is an interprime number because it is at equal distance from previous prime (161989819) and next prime (161989823).

It is not a de Polignac number, because 161989821 - 2¹ = 161989819 is a prime.

It is a super-2 number, since 2×161989821² = 52481404215224082, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (161989823) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 21996 + ... + 28421.

It is an arithmetic number, because the mean of its divisors is an integer number (9075240).

Almost surely, 2^161989821 is an apocalyptic number.

It is an amenable number.

161989821 is a deficient number, since it is larger than the sum of its proper divisors (128417859).

161989821 is a wasteful number, since it uses less digits than its factorization.

161989821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 50450 (or 50444 counting only the distinct ones).

The product of its digits is 62208, while the sum is 45.

The square root of 161989821 is about 12727.5221861916. The cubic root of 161989821 is about 545.1247600361.

The spelling of 161989821 in words is "one hundred sixty-one million, nine hundred eighty-nine thousand, eight hundred twenty-one".