21001851 has 24 divisors (see below), whose sum is σ = 34594560. Its totient is φ = 12162816.

The previous prime is 21001847. The next prime is 21001861. The reversal of 21001851 is 15810012.

It is not a de Polignac number, because 21001851 - 2² = 21001847 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21001801) 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 23 ways as a sum of consecutive naturals, for example, 3291 + ... + 7268.

It is an arithmetic number, because the mean of its divisors is an integer number (1441440).

Almost surely, 2^21001851 is an apocalyptic number.

21001851 is a deficient number, since it is larger than the sum of its proper divisors (13592709).

21001851 is a wasteful number, since it uses less digits than its factorization.

21001851 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10595 (or 10592 counting only the distinct ones).

The product of its (nonzero) digits is 80, while the sum is 18.

The square root of 21001851 is about 4582.7776511631. Note that the first 3 decimals coincide. The cubic root of 21001851 is about 275.9005233819.

Adding to 21001851 its reverse (15810012), we get a palindrome (36811863).

The spelling of 21001851 in words is "twenty-one million, one thousand, eight hundred fifty-one".