21212621 has 4 divisors (see below), whose sum is σ = 21730044. Its totient is φ = 20695200.

The previous prime is 21212603. The next prime is 21212623. The reversal of 21212621 is 12621212.

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 1729225 + 19483396 = 1315^2 + 4414^2 .

It is a cyclic number.

It is not a de Polignac number, because 21212621 - 2²² = 17018317 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21212621.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21212623) 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, 258650 + ... + 258731.

It is an arithmetic number, because the mean of its divisors is an integer number (5432511).

Almost surely, 2^21212621 is an apocalyptic number.

It is an amenable number.

21212621 is a deficient number, since it is larger than the sum of its proper divisors (517423).

21212621 is an equidigital number, since it uses as much as digits as its factorization.

21212621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 517422.

The product of its digits is 96, while the sum is 17.

The square root of 21212621 is about 4605.7161223853. The cubic root of 21212621 is about 276.8204121195.

Adding to 21212621 its reverse (12621212), we get a palindrome (33833833).

It can be divided in two parts, 2 and 1212621, that multiplied together give a palindrome (2425242).

The spelling of 21212621 in words is "twenty-one million, two hundred twelve thousand, six hundred twenty-one".