21728521836 has 120 divisors (see below), whose sum is σ = 65981950496. Its totient is φ = 6106337280.

The previous prime is 21728521819. The next prime is 21728521853. The reversal of 21728521836 is 63812582712.

21728521836 is a `hidden beast` number, since 21 + 7 + 28 + 521 + 83 + 6 = 666.

It is an interprime number because it is at equal distance from previous prime (21728521819) and next prime (21728521853).

It is a super-2 number, since 2×21728521836² (a number of 21 digits) contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21728521791 and 21728521800.

It is an unprimeable number.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 59820 + ... + 216876.

Almost surely, 2^21728521836 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21728521836, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32990975248).

21728521836 is an abundant number, since it is smaller than the sum of its proper divisors (44253428660).

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

21728521836 is a wasteful number, since it uses less digits than its factorization.

21728521836 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 157141 (or 157130 counting only the distinct ones).

The product of its digits is 322560, while the sum is 45.

It can be divided in two parts, 217285 and 21836, that added together give a square (239121 = 489²).

The spelling of 21728521836 in words is "twenty-one billion, seven hundred twenty-eight million, five hundred twenty-one thousand, eight hundred thirty-six".