21978284785 has 4 divisors (see below), whose sum is σ = 26373941748. Its totient is φ = 17582627824.

The previous prime is 21978284771. The next prime is 21978284837. The reversal of 21978284785 is 58748287912.

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

It can be written as a sum of positive squares in 2 ways, for example, as 4110348544 + 17867936241 = 64112^2 + 133671^2 .

It is a cyclic number.

It is not a de Polignac number, because 21978284785 - 2¹⁵ = 21978252017 is a prime.

It is a Duffinian number.

It is an unprimeable number.

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 3 ways as a sum of consecutive naturals, for example, 2197828474 + ... + 2197828483.

It is an arithmetic number, because the mean of its divisors is an integer number (6593485437).

Almost surely, 2^21978284785 is an apocalyptic number.

It is an amenable number.

21978284785 is a deficient number, since it is larger than the sum of its proper divisors (4395656963).

21978284785 is an equidigital number, since it uses as much as digits as its factorization.

21978284785 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4395656962.

The product of its digits is 18063360, while the sum is 61.

The spelling of 21978284785 in words is "twenty-one billion, nine hundred seventy-eight million, two hundred eighty-four thousand, seven hundred eighty-five".