21787028777 has 8 divisors (see below), whose sum is σ = 22124337960. Its totient is φ = 21450769920.

The previous prime is 21787028773. The next prime is 21787028789. The reversal of 21787028777 is 77782078712.

It can be written as a sum of positive squares in 4 ways, for example, as 477160336 + 21309868441 = 21844^2 + 145979^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21787028777 - 2² = 21787028773 is a prime.

It is a super-2 number, since 2×21787028777² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21787028773) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 220724 + ... + 303797.

It is an arithmetic number, because the mean of its divisors is an integer number (2765542245).

Almost surely, 2^21787028777 is an apocalyptic number.

It is an amenable number.

21787028777 is a deficient number, since it is larger than the sum of its proper divisors (337309183).

21787028777 is an equidigital number, since it uses as much as digits as its factorization.

21787028777 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 525163.

The product of its (nonzero) digits is 4302592, while the sum is 56.

The spelling of 21787028777 in words is "twenty-one billion, seven hundred eighty-seven million, twenty-eight thousand, seven hundred seventy-seven".