21405871 has 2 divisors, whose sum is σ = 21405872. Its totient is φ = 21405870.

The previous prime is 21405829. The next prime is 21405877. The reversal of 21405871 is 17850412.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21405871 - 2⁹ = 21405359 is a prime.

It is a super-2 number, since 2×21405871² = 916422626537282, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21405877) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10702935 + 10702936.

It is an arithmetic number, because the mean of its divisors is an integer number (10702936).

Almost surely, 2^21405871 is an apocalyptic number.

21405871 is a deficient number, since it is larger than the sum of its proper divisors (1).

21405871 is an equidigital number, since it uses as much as digits as its factorization.

21405871 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2240, while the sum is 28.

The square root of 21405871 is about 4626.6479226325. The cubic root of 21405871 is about 277.6584966918.

The spelling of 21405871 in words is "twenty-one million, four hundred five thousand, eight hundred seventy-one".