21605001 has 8 divisors (see below), whose sum is σ = 31425504. Its totient is φ = 13093920.

The previous prime is 21604997. The next prime is 21605009. The reversal of 21605001 is 10050612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21605001 - 2² = 21604997 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21605009) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 327316 + ... + 327381.

It is an arithmetic number, because the mean of its divisors is an integer number (3928188).

Almost surely, 2^21605001 is an apocalyptic number.

It is an amenable number.

21605001 is a deficient number, since it is larger than the sum of its proper divisors (9820503).

21605001 is a wasteful number, since it uses less digits than its factorization.

21605001 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 654711.

The product of its (nonzero) digits is 60, while the sum is 15.

The square root of 21605001 is about 4648.1180062473. The cubic root of 21605001 is about 278.5168214932.

Adding to 21605001 its reverse (10050612), we get a palindrome (31655613).

The spelling of 21605001 in words is "twenty-one million, six hundred five thousand, one".