21156571 has 4 divisors (see below), whose sum is σ = 21366144. Its totient is φ = 20947000.

The previous prime is 21156529. The next prime is 21156589. The reversal of 21156571 is 17565112.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21156571 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21156511) 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 in 3 ways as a sum of consecutive naturals, for example, 104635 + ... + 104836.

It is an arithmetic number, because the mean of its divisors is an integer number (5341536).

Almost surely, 2^21156571 is an apocalyptic number.

21156571 is a deficient number, since it is larger than the sum of its proper divisors (209573).

21156571 is a wasteful number, since it uses less digits than its factorization.

21156571 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 209572.

The product of its digits is 2100, while the sum is 28.

The square root of 21156571 is about 4599.6272675077. The cubic root of 21156571 is about 276.5763833413.

The spelling of 21156571 in words is "twenty-one million, one hundred fifty-six thousand, five hundred seventy-one".