21638329 has 2 divisors, whose sum is σ = 21638330. Its totient is φ = 21638328.

The previous prime is 21638327. The next prime is 21638339. The reversal of 21638329 is 92383612.

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., 12924025 + 8714304 = 3595^2 + 2952^2 .

It is a cyclic number.

It is not a de Polignac number, because 21638329 - 2¹ = 21638327 is a prime.

Together with 21638327, it forms a pair of twin primes.

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

It is a junction number, because it is equal to n+sod(n) for n = 21638294 and 21638303.

It is not a weakly prime, because it can be changed into another prime (21638327) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10819164 + 10819165.

It is an arithmetic number, because the mean of its divisors is an integer number (10819165).

Almost surely, 2^21638329 is an apocalyptic number.

It is an amenable number.

21638329 is a deficient number, since it is larger than the sum of its proper divisors (1).

21638329 is an equidigital number, since it uses as much as digits as its factorization.

21638329 is an evil number, because the sum of its binary digits is even.

The product of its digits is 15552, while the sum is 34.

The square root of 21638329 is about 4651.7017316247. The cubic root of 21638329 is about 278.6599618041.

It can be divided in two parts, 2163832 and 9, that added together give a square (2163841 = 1471²).

The spelling of 21638329 in words is "twenty-one million, six hundred thirty-eight thousand, three hundred twenty-nine".