21686555828 has 36 divisors (see below), whose sum is σ = 44156492100. Its totient is φ = 9292372992.

The previous prime is 21686555809. The next prime is 21686555831. The reversal of 21686555828 is 82855568612.

It can be written as a sum of positive squares in 2 ways, for example, as 20443852324 + 1242703504 = 142982^2 + 35252^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 1472276 + ... + 1486932.

It is an arithmetic number, because the mean of its divisors is an integer number (1226569225).

Almost surely, 2^21686555828 is an apocalyptic number.

21686555828 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

21686555828 is an abundant number, since it is smaller than the sum of its proper divisors (22469936272).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21686555828 is a wasteful number, since it uses less digits than its factorization.

21686555828 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22224 (or 22215 counting only the distinct ones).

The product of its digits is 9216000, while the sum is 56.

The spelling of 21686555828 in words is "twenty-one billion, six hundred eighty-six million, five hundred fifty-five thousand, eight hundred twenty-eight".