21000181 has 4 divisors (see below), whose sum is σ = 21031264. Its totient is φ = 20969100.

The previous prime is 21000169. The next prime is 21000191. The reversal of 21000181 is 18100012.

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 21000181 - 2⁹ = 20999669 is a prime.

It is a super-2 number, since 2×21000181² = 882015204065522, 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 (21000121) 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, 14505 + ... + 15886.

It is an arithmetic number, because the mean of its divisors is an integer number (5257816).

Almost surely, 2^21000181 is an apocalyptic number.

It is an amenable number.

21000181 is a deficient number, since it is larger than the sum of its proper divisors (31083).

21000181 is an equidigital number, since it uses as much as digits as its factorization.

21000181 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 31082.

The product of its (nonzero) digits is 16, while the sum is 13.

The square root of 21000181 is about 4582.5954436324. The cubic root of 21000181 is about 275.8932102791.

Adding to 21000181 its reverse (18100012), we get a palindrome (39100193).

The spelling of 21000181 in words is "twenty-one million, one hundred eighty-one", and thus it is an aban number.