21666829 has 2 divisors, whose sum is σ = 21666830. Its totient is φ = 21666828.

The previous prime is 21666817. The next prime is 21666863. The reversal of 21666829 is 92866612.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11744329 + 9922500 = 3427^2 + 3150^2 .

It is a cyclic number.

It is not a de Polignac number, because 21666829 - 2⁹ = 21666317 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21666791 and 21666800.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21666889) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10833414 + 10833415.

It is an arithmetic number, because the mean of its divisors is an integer number (10833415).

Almost surely, 2^21666829 is an apocalyptic number.

It is an amenable number.

21666829 is a deficient number, since it is larger than the sum of its proper divisors (1).

21666829 is an equidigital number, since it uses as much as digits as its factorization.

21666829 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 62208, while the sum is 40.

The square root of 21666829 is about 4654.7641186208. The cubic root of 21666829 is about 278.7822498163.

The spelling of 21666829 in words is "twenty-one million, six hundred sixty-six thousand, eight hundred twenty-nine".