21220621 has 4 divisors (see below), whose sum is σ = 21338044. Its totient is φ = 21103200.

The previous prime is 21220613. The next prime is 21220627. The reversal of 21220621 is 12602212.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 835396 + 20385225 = 914^2 + 4515^2 .

It is a cyclic number.

It is not a de Polignac number, because 21220621 - 2³ = 21220613 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21220595 and 21220604.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21220627) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 58440 + ... + 58801.

It is an arithmetic number, because the mean of its divisors is an integer number (5334511).

Almost surely, 2^21220621 is an apocalyptic number.

It is an amenable number.

21220621 is a deficient number, since it is larger than the sum of its proper divisors (117423).

21220621 is a wasteful number, since it uses less digits than its factorization.

21220621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 117422.

The product of its (nonzero) digits is 96, while the sum is 16.

The square root of 21220621 is about 4606.5845265229. The cubic root of 21220621 is about 276.8552072061.

Adding to 21220621 its reverse (12602212), we get a palindrome (33822833).

The spelling of 21220621 in words is "twenty-one million, two hundred twenty thousand, six hundred twenty-one".