21100001 has 4 divisors (see below), whose sum is σ = 22723092. Its totient is φ = 19476912.

The previous prime is 21099977. The next prime is 21100003. The reversal of 21100001 is 10000112.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 14592400 + 6507601 = 3820^2 + 2551^2 .

It is a de Polignac number, because none of the positive numbers 2^k-21100001 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21100003) 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, 811526 + ... + 811551.

It is an arithmetic number, because the mean of its divisors is an integer number (5680773).

Almost surely, 2^21100001 is an apocalyptic number.

It is an amenable number.

21100001 is a deficient number, since it is larger than the sum of its proper divisors (1623091).

21100001 is a wasteful number, since it uses less digits than its factorization.

21100001 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1623090.

The product of its (nonzero) digits is 2, while the sum is 5.

The square root of 21100001 is about 4593.4737399924. The cubic root of 21100001 is about 276.3296531909.

Adding to 21100001 its reverse (10000112), we get a palindrome (31100113).

Multiplying 21100001 by its reverse (10000112), we get a palindrome (211002373200112).

The spelling of 21100001 in words is "twenty-one million, one hundred thousand, one".