21009481 has 4 divisors (see below), whose sum is σ = 21109264. Its totient is φ = 20909700.

The previous prime is 21009449. The next prime is 21009491. The reversal of 21009481 is 18490012.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21009481 - 2⁵ = 21009449 is a prime.

It is a super-2 number, since 2×21009481² = 882796583778722, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21009491) 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, 49575 + ... + 49996.

It is an arithmetic number, because the mean of its divisors is an integer number (5277316).

Almost surely, 2^21009481 is an apocalyptic number.

It is an amenable number.

21009481 is a deficient number, since it is larger than the sum of its proper divisors (99783).

21009481 is an equidigital number, since it uses as much as digits as its factorization.

21009481 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 99782.

The product of its (nonzero) digits is 576, while the sum is 25.

The square root of 21009481 is about 4583.6100401321. The cubic root of 21009481 is about 275.9339310105.

Adding to 21009481 its reverse (18490012), we get a palindrome (39499493).

The spelling of 21009481 in words is "twenty-one million, nine thousand, four hundred eighty-one".