21001621 has 8 divisors (see below), whose sum is σ = 21855744. Its totient is φ = 20164560.

The previous prime is 21001577. The next prime is 21001627. The reversal of 21001621 is 12610012.

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

It is a cyclic number.

It is not a de Polignac number, because 21001621 - 2⁷ = 21001493 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21001627) 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, 1725 + ... + 6706.

It is an arithmetic number, because the mean of its divisors is an integer number (2731968).

Almost surely, 2^21001621 is an apocalyptic number.

It is an amenable number.

21001621 is a deficient number, since it is larger than the sum of its proper divisors (854123).

21001621 is an equidigital number, since it uses as much as digits as its factorization.

21001621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8531.

The product of its (nonzero) digits is 24, while the sum is 13.

The square root of 21001621 is about 4582.7525571429. The cubic root of 21001621 is about 275.8995162112.

Adding to 21001621 its reverse (12610012), we get a palindrome (33611633).

It can be divided in two parts, 2100 and 1621, that added together give a square (3721 = 61²).

The spelling of 21001621 in words is "twenty-one million, one thousand, six hundred twenty-one".