21109851 has 12 divisors (see below), whose sum is σ = 34848112. Its totient is φ = 12062736.

The previous prime is 21109841. The next prime is 21109867. The reversal of 21109851 is 15890112.

It is not a de Polignac number, because 21109851 - 2¹⁸ = 20847707 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21109841) 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, 167476 + ... + 167601.

Almost surely, 2^21109851 is an apocalyptic number.

21109851 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21109851 is a deficient number, since it is larger than the sum of its proper divisors (13738261).

21109851 is a wasteful number, since it uses less digits than its factorization.

21109851 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 335090 (or 335087 counting only the distinct ones).

The product of its (nonzero) digits is 720, while the sum is 27.

The square root of 21109851 is about 4594.5457882145. The cubic root of 21109851 is about 276.3726456636.

Adding to 21109851 its reverse (15890112), we get a palindrome (36999963).

The spelling of 21109851 in words is "twenty-one million, one hundred nine thousand, eight hundred fifty-one".