21667381 has 2 divisors, whose sum is σ = 21667382. Its totient is φ = 21667380.

The previous prime is 21667351. The next prime is 21667397. The reversal of 21667381 is 18376612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20848356 + 819025 = 4566^2 + 905^2 .

It is a cyclic number.

It is not a de Polignac number, because 21667381 - 2⁷ = 21667253 is a prime.

It is a super-2 number, since 2×21667381² = 938950798798322, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21667351) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10833690 + 10833691.

It is an arithmetic number, because the mean of its divisors is an integer number (10833691).

Almost surely, 2^21667381 is an apocalyptic number.

It is an amenable number.

21667381 is a deficient number, since it is larger than the sum of its proper divisors (1).

21667381 is an equidigital number, since it uses as much as digits as its factorization.

21667381 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 12096, while the sum is 34.

The square root of 21667381 is about 4654.8234123326. The cubic root of 21667381 is about 278.7846172831.

The spelling of 21667381 in words is "twenty-one million, six hundred sixty-seven thousand, three hundred eighty-one".