21687329 has 2 divisors, whose sum is σ = 21687330. Its totient is φ = 21687328.

The previous prime is 21687307. The next prime is 21687343. The reversal of 21687329 is 92378612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21641104 + 46225 = 4652^2 + 215^2 .

It is a cyclic number.

It is not a de Polignac number, because 21687329 - 2¹⁶ = 21621793 is a prime.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21687292 and 21687301.

It is not a weakly prime, because it can be changed into another prime (21617329) 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, 10843664 + 10843665.

It is an arithmetic number, because the mean of its divisors is an integer number (10843665).

Almost surely, 2^21687329 is an apocalyptic number.

It is an amenable number.

21687329 is a deficient number, since it is larger than the sum of its proper divisors (1).

21687329 is an equidigital number, since it uses as much as digits as its factorization.

21687329 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 36288, while the sum is 38.

The square root of 21687329 is about 4656.9656429912. The cubic root of 21687329 is about 278.8701450754.

The spelling of 21687329 in words is "twenty-one million, six hundred eighty-seven thousand, three hundred twenty-nine".