21571243 has 2 divisors, whose sum is σ = 21571244. Its totient is φ = 21571242.

The previous prime is 21571241. The next prime is 21571267. The reversal of 21571243 is 34217512.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21571243 - 2¹ = 21571241 is a prime.

Together with 21571241, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21571241) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10785621 + 10785622.

It is an arithmetic number, because the mean of its divisors is an integer number (10785622).

Almost surely, 2^21571243 is an apocalyptic number.

21571243 is a deficient number, since it is larger than the sum of its proper divisors (1).

21571243 is an equidigital number, since it uses as much as digits as its factorization.

21571243 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1680, while the sum is 25.

The square root of 21571243 is about 4644.4852244355. The cubic root of 21571243 is about 278.3716842307.

Adding to 21571243 its reverse (34217512), we get a palindrome (55788755).

The spelling of 21571243 in words is "twenty-one million, five hundred seventy-one thousand, two hundred forty-three".