21118421 has 6 divisors (see below), whose sum is σ = 21263970. Its totient is φ = 20973728.

The previous prime is 21118411. The next prime is 21118441. The reversal of 21118421 is 12481112.

It can be written as a sum of positive squares in 3 ways, for example, as 87025 + 21031396 = 295^2 + 4586^2 .

It is a de Polignac number, because none of the positive numbers 2^k-21118421 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21118393 and 21118402.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21118411) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 54095 + ... + 54483.

It is an arithmetic number, because the mean of its divisors is an integer number (3543995).

Almost surely, 2^21118421 is an apocalyptic number.

It is an amenable number.

21118421 is a deficient number, since it is larger than the sum of its proper divisors (145549).

21118421 is an frugal number, since it uses more digits than its factorization.

21118421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 855 (or 622 counting only the distinct ones).

The product of its digits is 128, while the sum is 20.

The square root of 21118421 is about 4595.4783211326. The cubic root of 21118421 is about 276.4100404187.

Adding to 21118421 its reverse (12481112), we get a palindrome (33599533).

The spelling of 21118421 in words is "twenty-one million, one hundred eighteen thousand, four hundred twenty-one".