21785851 has 2 divisors, whose sum is σ = 21785852. Its totient is φ = 21785850.

The previous prime is 21785849. The next prime is 21785867. The reversal of 21785851 is 15858712.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21785851 - 2¹ = 21785849 is a prime.

Together with 21785849, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 21785851.

It is not a weakly prime, because it can be changed into another prime (21785051) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10892925 + 10892926.

It is an arithmetic number, because the mean of its divisors is an integer number (10892926).

Almost surely, 2^21785851 is an apocalyptic number.

21785851 is a deficient number, since it is larger than the sum of its proper divisors (1).

21785851 is an equidigital number, since it uses as much as digits as its factorization.

21785851 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 22400, while the sum is 37.

The square root of 21785851 is about 4667.5315746120. The cubic root of 21785851 is about 279.2917944256.

It can be divided in two parts, 217 and 85851, that added together give a palindrome (86068).

The spelling of 21785851 in words is "twenty-one million, seven hundred eighty-five thousand, eight hundred fifty-one".