21004001 has 4 divisors (see below), whose sum is σ = 21299904. Its totient is φ = 20708100.

The previous prime is 21003937. The next prime is 21004043. The reversal of 21004001 is 10040012.

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 21004001 - 2⁶ = 21003937 is a prime.

It is a super-3 number, since 3×21004001³ (a number of 23 digits) contains 333 as substring.

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 21004001.

It is not an unprimeable number, because it can be changed into a prime (21004301) 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, 147845 + ... + 147986.

It is an arithmetic number, because the mean of its divisors is an integer number (5324976).

Almost surely, 2^21004001 is an apocalyptic number.

It is an amenable number.

21004001 is a deficient number, since it is larger than the sum of its proper divisors (295903).

21004001 is an equidigital number, since it uses as much as digits as its factorization.

21004001 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 295902.

The product of its (nonzero) digits is 8, while the sum is 8.

The square root of 21004001 is about 4583.0122190542. The cubic root of 21004001 is about 275.9099378836.

Adding to 21004001 its reverse (10040012), we get a palindrome (31044013).

It can be divided in two parts, 2 and 1004001, that multiplied together give a palindrome (2008002).

The spelling of 21004001 in words is "twenty-one million, four thousand, one".