21000001 has 4 divisors (see below), whose sum is σ = 22909104. Its totient is φ = 19090900.

The previous prime is 20999999. The next prime is 21000037. The reversal of 21000001 is 10000012.

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 21000001 - 2¹ = 20999999 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21000041) 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, 954535 + ... + 954556.

It is an arithmetic number, because the mean of its divisors is an integer number (5727276).

Almost surely, 2^21000001 is an apocalyptic number.

It is an amenable number.

21000001 is a deficient number, since it is larger than the sum of its proper divisors (1909103).

21000001 is a wasteful number, since it uses less digits than its factorization.

21000001 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1909102.

The product of its (nonzero) digits is 2, while the sum is 4.

The square root of 21000001 is about 4582.5758040648. The cubic root of 21000001 is about 275.8924220174.

Adding to 21000001 its reverse (10000012), we get a palindrome (31000013).

Multiplying 21000001 by its reverse (10000012), we get a palindrome (210000262000012).

It can be divided in two parts, 2 and 1000001, that multiplied together give a palindrome (2000002).

The spelling of 21000001 in words is "twenty-one million, one", and thus it is an aban number and an uban number.