21872161 has 4 divisors (see below), whose sum is σ = 21883072. Its totient is φ = 21861252.

The previous prime is 21872159. The next prime is 21872171. The reversal of 21872161 is 16127812.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21872161 - 2¹ = 21872159 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21872171) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1485 + ... + 6778.

It is an arithmetic number, because the mean of its divisors is an integer number (5470768).

Almost surely, 2^21872161 is an apocalyptic number.

It is an amenable number.

21872161 is a deficient number, since it is larger than the sum of its proper divisors (10911).

21872161 is an equidigital number, since it uses as much as digits as its factorization.

21872161 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10910.

The product of its digits is 1344, while the sum is 28.

The square root of 21872161 is about 4676.7682217531. The cubic root of 21872161 is about 279.6601361096.

Adding to 21872161 its reverse (16127812), we get a palindrome (37999973).

The spelling of 21872161 in words is "twenty-one million, eight hundred seventy-two thousand, one hundred sixty-one".