21005161 has 4 divisors (see below), whose sum is σ = 21517524. Its totient is φ = 20492800.

The previous prime is 21005143. The next prime is 21005177. The reversal of 21005161 is 16150012.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 755161 + 20250000 = 869^2 + 4500^2 .

It is a cyclic number.

It is not a de Polignac number, because 21005161 - 2⁵ = 21005129 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21005111) 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, 256120 + ... + 256201.

It is an arithmetic number, because the mean of its divisors is an integer number (5379381).

Almost surely, 2^21005161 is an apocalyptic number.

It is an amenable number.

21005161 is a deficient number, since it is larger than the sum of its proper divisors (512363).

21005161 is an equidigital number, since it uses as much as digits as its factorization.

21005161 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 512362.

The product of its (nonzero) digits is 60, while the sum is 16.

The square root of 21005161 is about 4583.1387716280. The cubic root of 21005161 is about 275.9150170689.

Adding to 21005161 its reverse (16150012), we get a palindrome (37155173).

The spelling of 21005161 in words is "twenty-one million, five thousand, one hundred sixty-one".