21081621 has 16 divisors (see below), whose sum is σ = 32279040. Its totient is φ = 12103920.

The previous prime is 21081611. The next prime is 21081623. The reversal of 21081621 is 12618012.

It is not a de Polignac number, because 21081621 - 2⁵ = 21081589 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21081623) 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 15 ways as a sum of consecutive naturals, for example, 16185 + ... + 17438.

It is an arithmetic number, because the mean of its divisors is an integer number (2017440).

Almost surely, 2^21081621 is an apocalyptic number.

It is an amenable number.

21081621 is a deficient number, since it is larger than the sum of its proper divisors (11197419).

21081621 is a wasteful number, since it uses less digits than its factorization.

21081621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 33656.

The product of its (nonzero) digits is 192, while the sum is 21.

The square root of 21081621 is about 4591.4726395787. The cubic root of 21081621 is about 276.2493938822.

Adding to 21081621 its reverse (12618012), we get a palindrome (33699633).

The spelling of 21081621 in words is "twenty-one million, eighty-one thousand, six hundred twenty-one".