21366181 has 2 divisors, whose sum is σ = 21366182. Its totient is φ = 21366180.

The previous prime is 21366179. The next prime is 21366187. The reversal of 21366181 is 18166312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14130081 + 7236100 = 3759^2 + 2690^2 .

It is a cyclic number.

It is not a de Polignac number, because 21366181 - 2¹ = 21366179 is a prime.

It is a super-2 number, since 2×21366181² = 913027381049522, which contains 22 as substring.

Together with 21366179, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21366187) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10683090 + 10683091.

It is an arithmetic number, because the mean of its divisors is an integer number (10683091).

Almost surely, 2^21366181 is an apocalyptic number.

It is an amenable number.

21366181 is a deficient number, since it is larger than the sum of its proper divisors (1).

21366181 is an equidigital number, since it uses as much as digits as its factorization.

21366181 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1728, while the sum is 28.

The square root of 21366181 is about 4622.3566500217. The cubic root of 21366181 is about 277.4867823697.

The spelling of 21366181 in words is "twenty-one million, three hundred sixty-six thousand, one hundred eighty-one".