21687565536 has 768 divisors, whose sum is σ = 82910822400. Its totient is φ = 5359343616.

The previous prime is 21687565531. The next prime is 21687565541. The reversal of 21687565536 is 63556578612.

It is a happy number.

21687565536 is a `hidden beast` number, since 2 + 1 + 6 + 87 + 5 + 6 + 553 + 6 = 666.

It is an interprime number because it is at equal distance from previous prime (21687565531) and next prime (21687565541).

It is a Harshad number since it is a multiple of its sum of digits (54).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21687565531) by changing a digit.

It is a polite number, since it can be written in 127 ways as a sum of consecutive naturals, for example, 121159495 + ... + 121159673.

It is an arithmetic number, because the mean of its divisors is an integer number (107956800).

Almost surely, 2^21687565536 is an apocalyptic number.

21687565536 is a gapful number since it is divisible by the number (26) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21687565536, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (41455411200).

21687565536 is an abundant number, since it is smaller than the sum of its proper divisors (61223256864).

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

21687565536 is a wasteful number, since it uses less digits than its factorization.

21687565536 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 308 (or 294 counting only the distinct ones).

The product of its digits is 9072000, while the sum is 54.

The spelling of 21687565536 in words is "twenty-one billion, six hundred eighty-seven million, five hundred sixty-five thousand, five hundred thirty-six".