21187771 has 4 divisors (see below), whose sum is σ = 23113944. Its totient is φ = 19261600.

The previous prime is 21187759. The next prime is 21187781. The reversal of 21187771 is 17778112.

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

It is a cyclic number.

It is not a de Polignac number, because 21187771 - 2⁹ = 21187259 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21187781) 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, 963070 + ... + 963091.

It is an arithmetic number, because the mean of its divisors is an integer number (5778486).

Almost surely, 2^21187771 is an apocalyptic number.

21187771 is a deficient number, since it is larger than the sum of its proper divisors (1926173).

21187771 is a wasteful number, since it uses less digits than its factorization.

21187771 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1926172.

The product of its digits is 5488, while the sum is 34.

The square root of 21187771 is about 4603.0175971856. The cubic root of 21187771 is about 276.7122740575.

It can be divided in two parts, 2118 and 7771, that added together give a palindrome (9889).

The spelling of 21187771 in words is "twenty-one million, one hundred eighty-seven thousand, seven hundred seventy-one".