21395971 has 4 divisors (see below), whose sum is σ = 21406000. Its totient is φ = 21385944.

The previous prime is 21395963. The next prime is 21395987. The reversal of 21395971 is 17959312.

21395971 is nontrivially palindromic in base 12.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21395971 - 2³ = 21395963 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21395971.

It is not an unprimeable number, because it can be changed into a prime (21395771) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 396 + ... + 6553.

It is an arithmetic number, because the mean of its divisors is an integer number (5351500).

Almost surely, 2^21395971 is an apocalyptic number.

21395971 is a deficient number, since it is larger than the sum of its proper divisors (10029).

21395971 is an equidigital number, since it uses as much as digits as its factorization.

21395971 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10028.

The product of its digits is 17010, while the sum is 37.

The square root of 21395971 is about 4625.5779098400. The cubic root of 21395971 is about 277.6156853373.

It can be divided in two parts, 21395 and 971, that added together give a triangular number (22366 = T₂₁₁).

The spelling of 21395971 in words is "twenty-one million, three hundred ninety-five thousand, nine hundred seventy-one".