21642161 has 4 divisors (see below), whose sum is σ = 21798000. Its totient is φ = 21486324.

The previous prime is 21642143. The next prime is 21642169. The reversal of 21642161 is 16124612.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21642161 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21642169) 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, 77711 + ... + 77988.

It is an arithmetic number, because the mean of its divisors is an integer number (5449500).

Almost surely, 2^21642161 is an apocalyptic number.

It is an amenable number.

21642161 is a deficient number, since it is larger than the sum of its proper divisors (155839).

21642161 is a wasteful number, since it uses less digits than its factorization.

21642161 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 155838.

The product of its digits is 576, while the sum is 23.

The square root of 21642161 is about 4652.1136056636. The cubic root of 21642161 is about 278.6764104240.

Adding to 21642161 its reverse (16124612), we get a palindrome (37766773).

The spelling of 21642161 in words is "twenty-one million, six hundred forty-two thousand, one hundred sixty-one".