21408971 has 2 divisors, whose sum is σ = 21408972. Its totient is φ = 21408970.

The previous prime is 21408949. The next prime is 21408973. The reversal of 21408971 is 17980412.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21408971 - 2¹⁴ = 21392587 is a prime.

Together with 21408973, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21408973) 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, 10704485 + 10704486.

It is an arithmetic number, because the mean of its divisors is an integer number (10704486).

Almost surely, 2^21408971 is an apocalyptic number.

21408971 is a deficient number, since it is larger than the sum of its proper divisors (1).

21408971 is an equidigital number, since it uses as much as digits as its factorization.

21408971 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 4032, while the sum is 32.

The square root of 21408971 is about 4626.9829262706. The cubic root of 21408971 is about 277.6718995536.

It can be divided in two parts, 2140 and 8971, that added together give a palindrome (11111).

The spelling of 21408971 in words is "twenty-one million, four hundred eight thousand, nine hundred seventy-one".