21405887 has 2 divisors, whose sum is σ = 21405888. Its totient is φ = 21405886.

The previous prime is 21405877. The next prime is 21405889. The reversal of 21405887 is 78850412.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21405887 - 2⁴ = 21405871 is a prime.

Together with 21405889, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21405889) 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, 10702943 + 10702944.

It is an arithmetic number, because the mean of its divisors is an integer number (10702944).

Almost surely, 2^21405887 is an apocalyptic number.

21405887 is a deficient number, since it is larger than the sum of its proper divisors (1).

21405887 is an equidigital number, since it uses as much as digits as its factorization.

21405887 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 17920, while the sum is 35.

The square root of 21405887 is about 4626.6496517459. The cubic root of 21405887 is about 277.6585658712.

The spelling of 21405887 in words is "twenty-one million, four hundred five thousand, eight hundred eighty-seven".