21642065 has 4 divisors (see below), whose sum is σ = 25970484. Its totient is φ = 17313648.

The previous prime is 21642017. The next prime is 21642067. The reversal of 21642065 is 56024612.

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

It can be written as a sum of positive squares in 2 ways, for example, as 7929856 + 13712209 = 2816^2 + 3703^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21642065 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21642067) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2164202 + ... + 2164211.

It is an arithmetic number, because the mean of its divisors is an integer number (6492621).

Almost surely, 2^21642065 is an apocalyptic number.

It is an amenable number.

21642065 is a deficient number, since it is larger than the sum of its proper divisors (4328419).

21642065 is an equidigital number, since it uses as much as digits as its factorization.

21642065 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4328418.

The product of its (nonzero) digits is 2880, while the sum is 26.

The square root of 21642065 is about 4652.1032877614. The cubic root of 21642065 is about 278.6759983737.

Adding to 21642065 its reverse (56024612), we get a palindrome (77666677).

The spelling of 21642065 in words is "twenty-one million, six hundred forty-two thousand, sixty-five".