21003851 has 4 divisors (see below), whose sum is σ = 22913304. Its totient is φ = 19094400.

The previous prime is 21003821. The next prime is 21003869. The reversal of 21003851 is 15830012.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21003851 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21003811) 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, 954710 + ... + 954731.

It is an arithmetic number, because the mean of its divisors is an integer number (5728326).

Almost surely, 2^21003851 is an apocalyptic number.

21003851 is a deficient number, since it is larger than the sum of its proper divisors (1909453).

21003851 is a wasteful number, since it uses less digits than its factorization.

21003851 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1909452.

The product of its (nonzero) digits is 240, while the sum is 20.

The square root of 21003851 is about 4582.9958542421. The cubic root of 21003851 is about 275.9092810788.

Adding to 21003851 its reverse (15830012), we get a palindrome (36833863).

The spelling of 21003851 in words is "twenty-one million, three thousand, eight hundred fifty-one".