21638249 has 2 divisors, whose sum is σ = 21638250. Its totient is φ = 21638248.

The previous prime is 21638231. The next prime is 21638273. The reversal of 21638249 is 94283612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17808400 + 3829849 = 4220^2 + 1957^2 .

It is a cyclic number.

It is not a de Polignac number, because 21638249 - 2¹² = 21634153 is a prime.

It is a Chen prime.

It is equal to p_1367774 and since 21638249 and 1367774 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (21638219) 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, 10819124 + 10819125.

It is an arithmetic number, because the mean of its divisors is an integer number (10819125).

Almost surely, 2^21638249 is an apocalyptic number.

It is an amenable number.

21638249 is a deficient number, since it is larger than the sum of its proper divisors (1).

21638249 is an equidigital number, since it uses as much as digits as its factorization.

21638249 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 20736, while the sum is 35.

The square root of 21638249 is about 4651.6931326131. The cubic root of 21638249 is about 278.6596183884.

The spelling of 21638249 in words is "twenty-one million, six hundred thirty-eight thousand, two hundred forty-nine".