161216021 has 4 divisors (see below), whose sum is σ = 161245344. Its totient is φ = 161186700.

The previous prime is 161216009. The next prime is 161216023. The reversal of 161216021 is 120612161.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 161216021 - 2¹⁰ = 161214997 is a prime.

It is a deceptive number, since it divides R_161216020.

It is a Duffinian number.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 161215984 and 161216002.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (161216023) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3665 + ... + 18326.

It is an arithmetic number, because the mean of its divisors is an integer number (40311336).

It is a Poulet number, since it divides 2^161216020-1.

Almost surely, 2^161216021 is an apocalyptic number.

161216021 is the 7331-st octagonal number.

It is an amenable number.

161216021 is a deficient number, since it is larger than the sum of its proper divisors (29323).

161216021 is an equidigital number, since it uses as much as digits as its factorization.

161216021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 29322.

The product of its (nonzero) digits is 144, while the sum is 20.

The square root of 161216021 is about 12697.0871068919. The cubic root of 161216021 is about 544.2553824070.

Adding to 161216021 its reverse (120612161), we get a palindrome (281828182).

The spelling of 161216021 in words is "one hundred sixty-one million, two hundred sixteen thousand, twenty-one".