21171813 has 12 divisors (see below), whose sum is σ = 30568320. Its totient is φ = 13028496.

The previous prime is 21171811. The next prime is 21171823. The reversal of 21171813 is 31817112.

It is a happy number.

It is not a de Polignac number, because 21171813 - 2¹ = 21171811 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21171811) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 20373 + ... + 21386.

It is an arithmetic number, because the mean of its divisors is an integer number (2547360).

Almost surely, 2^21171813 is an apocalyptic number.

It is an amenable number.

21171813 is a deficient number, since it is larger than the sum of its proper divisors (9396507).

21171813 is a wasteful number, since it uses less digits than its factorization.

21171813 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 41788 (or 41775 counting only the distinct ones).

The product of its digits is 336, while the sum is 24.

The square root of 21171813 is about 4601.2838425813. The cubic root of 21171813 is about 276.6427861196.

Adding to 21171813 its reverse (31817112), we get a palindrome (52988925).

The spelling of 21171813 in words is "twenty-one million, one hundred seventy-one thousand, eight hundred thirteen".