21123871 has 2 divisors, whose sum is σ = 21123872. Its totient is φ = 21123870.

The previous prime is 21123863. The next prime is 21123887. The reversal of 21123871 is 17832112.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21123871 - 2³ = 21123863 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21123841) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10561935 + 10561936.

It is an arithmetic number, because the mean of its divisors is an integer number (10561936).

Almost surely, 2^21123871 is an apocalyptic number.

21123871 is a deficient number, since it is larger than the sum of its proper divisors (1).

21123871 is an equidigital number, since it uses as much as digits as its factorization.

21123871 is an evil number, because the sum of its binary digits is even.

The product of its digits is 672, while the sum is 25.

The square root of 21123871 is about 4596.0712570629. The cubic root of 21123871 is about 276.4338159518.

Adding to 21123871 its reverse (17832112), we get a palindrome (38955983).

The spelling of 21123871 in words is "twenty-one million, one hundred twenty-three thousand, eight hundred seventy-one".