21447 has 6 divisors (see below), whose sum is σ = 30992. Its totient is φ = 14292.

The previous prime is 21433. The next prime is 21467. The reversal of 21447 is 74412.

It is a happy number.

It is not a de Polignac number, because 21447 - 2⁶ = 21383 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 21447.

It is not an unprimeable number, because it can be changed into a prime (21407) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1183 + ... + 1200.

2²¹⁴⁴⁷ is an apocalyptic number.

21447 is a deficient number, since it is larger than the sum of its proper divisors (9545).

21447 is a wasteful number, since it uses less digits than its factorization.

21447 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2389 (or 2386 counting only the distinct ones).

The product of its digits is 224, while the sum is 18.

The square root of 21447 is about 146.4479429695. The cubic root of 21447 is about 27.7836212892.

Adding to 21447 its reverse (74412), we get a palindrome (95859).

The spelling of 21447 in words is "twenty-one thousand, four hundred forty-seven", and thus it is an iban number.