21784491851 has 2 divisors, whose sum is σ = 21784491852. Its totient is φ = 21784491850.

The previous prime is 21784491847. The next prime is 21784491983. The reversal of 21784491851 is 15819448712.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21784491851 - 2² = 21784491847 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21784491851.

It is not a weakly prime, because it can be changed into another prime (21784491811) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10892245925 + 10892245926.

It is an arithmetic number, because the mean of its divisors is an integer number (10892245926).

Almost surely, 2^21784491851 is an apocalyptic number.

21784491851 is a deficient number, since it is larger than the sum of its proper divisors (1).

21784491851 is an equidigital number, since it uses as much as digits as its factorization.

21784491851 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 645120, while the sum is 50.

The spelling of 21784491851 in words is "twenty-one billion, seven hundred eighty-four million, four hundred ninety-one thousand, eight hundred fifty-one".