21609439 has 2 divisors, whose sum is σ = 21609440. Its totient is φ = 21609438.

The previous prime is 21609407. The next prime is 21609461. The reversal of 21609439 is 93490612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21609439 - 2⁵ = 21609407 is a prime.

It is a plaindrome in base 16.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21609239) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10804719 + 10804720.

It is an arithmetic number, because the mean of its divisors is an integer number (10804720).

Almost surely, 2^21609439 is an apocalyptic number.

21609439 is a deficient number, since it is larger than the sum of its proper divisors (1).

21609439 is an equidigital number, since it uses as much as digits as its factorization.

21609439 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 11664, while the sum is 34.

The square root of 21609439 is about 4648.5953792517. The cubic root of 21609439 is about 278.5358907360.

The spelling of 21609439 in words is "twenty-one million, six hundred nine thousand, four hundred thirty-nine".