21811851 has 6 divisors (see below), whose sum is σ = 31506020. Its totient is φ = 14541228.

The previous prime is 21811849. The next prime is 21811861. The reversal of 21811851 is 15811812.

It is not a de Polignac number, because 21811851 - 2¹ = 21811849 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21811861) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1211761 + ... + 1211778.

Almost surely, 2^21811851 is an apocalyptic number.

21811851 is a deficient number, since it is larger than the sum of its proper divisors (9694169).

21811851 is a wasteful number, since it uses less digits than its factorization.

21811851 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2423545 (or 2423542 counting only the distinct ones).

The product of its digits is 640, while the sum is 27.

The square root of 21811851 is about 4670.3159422035. The cubic root of 21811851 is about 279.4028558024.

The spelling of 21811851 in words is "twenty-one million, eight hundred eleven thousand, eight hundred fifty-one".