21004121 has 4 divisors (see below), whose sum is σ = 21014544. Its totient is φ = 20993700.

The previous prime is 21004117. The next prime is 21004153. The reversal of 21004121 is 12140012.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21004121 - 2² = 21004117 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21004721) 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 3 ways as a sum of consecutive naturals, for example, 1115 + ... + 6576.

It is an arithmetic number, because the mean of its divisors is an integer number (5253636).

Almost surely, 2^21004121 is an apocalyptic number.

It is an amenable number.

21004121 is a deficient number, since it is larger than the sum of its proper divisors (10423).

21004121 is an equidigital number, since it uses as much as digits as its factorization.

21004121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10422.

The product of its (nonzero) digits is 16, while the sum is 11.

The square root of 21004121 is about 4583.0253108618. The cubic root of 21004121 is about 275.9104633253.

Adding to 21004121 its reverse (12140012), we get a palindrome (33144133).

The spelling of 21004121 in words is "twenty-one million, four thousand, one hundred twenty-one".