21517439 has 2 divisors, whose sum is σ = 21517440. Its totient is φ = 21517438.

The previous prime is 21517429. The next prime is 21517451. The reversal of 21517439 is 93471512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21517439 - 2²⁰ = 20468863 is a prime.

It is a super-2 number, since 2×21517439² = 926000362237442, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21517429) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10758719 + 10758720.

It is an arithmetic number, because the mean of its divisors is an integer number (10758720).

Almost surely, 2^21517439 is an apocalyptic number.

21517439 is a deficient number, since it is larger than the sum of its proper divisors (1).

21517439 is an equidigital number, since it uses as much as digits as its factorization.

21517439 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 7560, while the sum is 32.

The square root of 21517439 is about 4638.6893623091. The cubic root of 21517439 is about 278.1400489942.

The spelling of 21517439 in words is "twenty-one million, five hundred seventeen thousand, four hundred thirty-nine".