21109381 has 2 divisors, whose sum is σ = 21109382. Its totient is φ = 21109380.

The previous prime is 21109369. The next prime is 21109391. The reversal of 21109381 is 18390112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20784481 + 324900 = 4559^2 + 570^2 .

It is a cyclic number.

It is not a de Polignac number, because 21109381 - 2⁹ = 21108869 is a prime.

It is a super-2 number, since 2×21109381² = 891211932406322, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21109321) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10554690 + 10554691.

It is an arithmetic number, because the mean of its divisors is an integer number (10554691).

Almost surely, 2^21109381 is an apocalyptic number.

It is an amenable number.

21109381 is a deficient number, since it is larger than the sum of its proper divisors (1).

21109381 is an equidigital number, since it uses as much as digits as its factorization.

21109381 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 432, while the sum is 25.

The square root of 21109381 is about 4594.4946403277. The cubic root of 21109381 is about 276.3705945500.

Adding to 21109381 its reverse (18390112), we get a palindrome (39499493).

The spelling of 21109381 in words is "twenty-one million, one hundred nine thousand, three hundred eighty-one".