21612005 has 4 divisors (see below), whose sum is σ = 25934412. Its totient is φ = 17289600.

The previous prime is 21611999. The next prime is 21612011. The reversal of 21612005 is 50021612.

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

It is an interprime number because it is at equal distance from previous prime (21611999) and next prime (21612011).

It can be written as a sum of positive squares in 2 ways, for example, as 13535041 + 8076964 = 3679^2 + 2842^2 .

It is not a de Polignac number, because 21612005 - 2¹⁴ = 21595621 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

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, 2161196 + ... + 2161205.

It is an arithmetic number, because the mean of its divisors is an integer number (6483603).

Almost surely, 2^21612005 is an apocalyptic number.

It is an amenable number.

21612005 is a deficient number, since it is larger than the sum of its proper divisors (4322407).

21612005 is an equidigital number, since it uses as much as digits as its factorization.

21612005 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4322406.

The product of its (nonzero) digits is 120, while the sum is 17.

The square root of 21612005 is about 4648.8713684076. The cubic root of 21612005 is about 278.5469151593.

Adding to 21612005 its reverse (50021612), we get a palindrome (71633617).

It can be divided in two parts, 216 and 12005, that added together give a palindrome (12221).

The spelling of 21612005 in words is "twenty-one million, six hundred twelve thousand, five".