21628181 has 4 divisors (see below), whose sum is σ = 21637932. Its totient is φ = 21618432.

The previous prime is 21628169. The next prime is 21628193. The reversal of 21628181 is 18182612.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is an interprime number because it is at equal distance from previous prime (21628169) and next prime (21628193).

It can be written as a sum of positive squares in 2 ways, for example, as 14945956 + 6682225 = 3866^2 + 2585^2 .

It is a cyclic number.

It is not a de Polignac number, because 21628181 - 2¹⁰ = 21627157 is a prime.

It is a super-2 number, since 2×21628181² = 935556426737522, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21628121) 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, 245 + ... + 6581.

It is an arithmetic number, because the mean of its divisors is an integer number (5409483).

Almost surely, 2^21628181 is an apocalyptic number.

It is an amenable number.

21628181 is a deficient number, since it is larger than the sum of its proper divisors (9751).

21628181 is an equidigital number, since it uses as much as digits as its factorization.

21628181 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9750.

The product of its digits is 1536, while the sum is 29.

The square root of 21628181 is about 4650.6108200966. The cubic root of 21628181 is about 278.6163927670.

The spelling of 21628181 in words is "twenty-one million, six hundred twenty-eight thousand, one hundred eighty-one".