21113621 has 4 divisors (see below), whose sum is σ = 21223212. Its totient is φ = 21004032.

The previous prime is 21113611. The next prime is 21113629. The reversal of 21113621 is 12631112.

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 13764100 + 7349521 = 3710^2 + 2711^2 .

It is a cyclic number.

It is not a de Polignac number, because 21113621 - 2¹⁸ = 20851477 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21113621.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21113629) 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, 54506 + ... + 54891.

It is an arithmetic number, because the mean of its divisors is an integer number (5305803).

Almost surely, 2^21113621 is an apocalyptic number.

It is an amenable number.

21113621 is a deficient number, since it is larger than the sum of its proper divisors (109591).

21113621 is a wasteful number, since it uses less digits than its factorization.

21113621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 109590.

The product of its digits is 72, while the sum is 17.

The square root of 21113621 is about 4594.9560389627. The cubic root of 21113621 is about 276.3890971117.

Adding to 21113621 its reverse (12631112), we get a palindrome (33744733).

The spelling of 21113621 in words is "twenty-one million, one hundred thirteen thousand, six hundred twenty-one".