21042621 has 12 divisors (see below), whose sum is σ = 30893980. Its totient is φ = 13798080.

The previous prime is 21042601. The next prime is 21042629. The reversal of 21042621 is 12624012.

21042621 is a `hidden beast` number, since 2 + 1 + 0 + 42 + 621 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 4347225 + 16695396 = 2085^2 + 4086^2 .

It is not a de Polignac number, because 21042621 - 2¹⁴ = 21026237 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21042594 and 21042603.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21042629) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 18616 + ... + 19713.

Almost surely, 2^21042621 is an apocalyptic number.

It is an amenable number.

21042621 is a deficient number, since it is larger than the sum of its proper divisors (9851359).

21042621 is a wasteful number, since it uses less digits than its factorization.

21042621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 38396 (or 38393 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 18.

The square root of 21042621 is about 4587.2236701517. The cubic root of 21042621 is about 276.0789392980.

Adding to 21042621 its reverse (12624012), we get a palindrome (33666633).

The spelling of 21042621 in words is "twenty-one million, forty-two thousand, six hundred twenty-one".