21898181 has 2 divisors, whose sum is σ = 21898182. Its totient is φ = 21898180.

The previous prime is 21898153. The next prime is 21898187. The reversal of 21898181 is 18189812.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19228225 + 2669956 = 4385^2 + 1634^2 .

It is a cyclic number.

It is not a de Polignac number, because 21898181 - 2¹⁸ = 21636037 is a prime.

It is a super-2 number, since 2×21898181² = 959060662217522, which contains 22 as substring.

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

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21898187) by changing a digit.

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10949090 + 10949091.

It is an arithmetic number, because the mean of its divisors is an integer number (10949091).

Almost surely, 2^21898181 is an apocalyptic number.

It is an amenable number.

21898181 is a deficient number, since it is larger than the sum of its proper divisors (1).

21898181 is an equidigital number, since it uses as much as digits as its factorization.

21898181 is an evil number, because the sum of its binary digits is even.

The product of its digits is 9216, while the sum is 38.

The square root of 21898181 is about 4679.5492304281. The cubic root of 21898181 is about 279.7709904673.

The spelling of 21898181 in words is "twenty-one million, eight hundred ninety-eight thousand, one hundred eighty-one".