21771439 has 2 divisors, whose sum is σ = 21771440. Its totient is φ = 21771438.

The previous prime is 21771437. The next prime is 21771443. The reversal of 21771439 is 93417712.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21771439 - 2¹ = 21771437 is a prime.

It is a super-2 number, since 2×21771439² = 947991112261442, which contains 22 as substring.

Together with 21771437, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21771437) 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, 10885719 + 10885720.

It is an arithmetic number, because the mean of its divisors is an integer number (10885720).

Almost surely, 2^21771439 is an apocalyptic number.

21771439 is a deficient number, since it is larger than the sum of its proper divisors (1).

21771439 is an equidigital number, since it uses as much as digits as its factorization.

21771439 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 10584, while the sum is 34.

The square root of 21771439 is about 4665.9874624778. The cubic root of 21771439 is about 279.2301941809.

The spelling of 21771439 in words is "twenty-one million, seven hundred seventy-one thousand, four hundred thirty-nine".