21501621 has 12 divisors (see below), whose sum is σ = 31257772. Its totient is φ = 14242176.

The previous prime is 21501593. The next prime is 21501643. The reversal of 21501621 is 12610512.

It can be written as a sum of positive squares in 2 ways, for example, as 12680721 + 8820900 = 3561^2 + 2970^2 .

It is not a de Polignac number, because 21501621 - 2¹⁷ = 21370549 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21501594 and 21501603.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21501661) 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 11 ways as a sum of consecutive naturals, for example, 6196 + ... + 9021.

Almost surely, 2^21501621 is an apocalyptic number.

It is an amenable number.

21501621 is a deficient number, since it is larger than the sum of its proper divisors (9756151).

21501621 is a wasteful number, since it uses less digits than its factorization.

21501621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15380 (or 15377 counting only the distinct ones).

The product of its (nonzero) digits is 120, while the sum is 18.

The square root of 21501621 is about 4636.9840413786. The cubic root of 21501621 is about 278.0718764169.

It can be divided in two parts, 21501 and 621, that added together give a palindrome (22122).

The spelling of 21501621 in words is "twenty-one million, five hundred one thousand, six hundred twenty-one".