21855616020 has 720 divisors, whose sum is σ = 86160634560. Its totient is φ = 4608866304.

The previous prime is 21855616009. The next prime is 21855616031. The reversal of 21855616020 is 2061655812.

21855616020 is a `hidden beast` number, since 2 + 18 + 5 + 5 + 616 + 0 + 20 = 666.

It is an interprime number because it is at equal distance from previous prime (21855616009) and next prime (21855616031).

It is a super-2 number, since 2×21855616020² (a number of 21 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 239 ways as a sum of consecutive naturals, for example, 64853292 + ... + 64853628.

It is an arithmetic number, because the mean of its divisors is an integer number (119667548).

Almost surely, 2^21855616020 is an apocalyptic number.

21855616020 is a gapful number since it is divisible by the number (20) 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 21855616020, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (43080317280).

21855616020 is an abundant number, since it is smaller than the sum of its proper divisors (64305018540).

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

21855616020 is a wasteful number, since it uses less digits than its factorization.

21855616020 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 434 (or 416 counting only the distinct ones).

The product of its (nonzero) digits is 28800, while the sum is 36.

The spelling of 21855616020 in words is "twenty-one billion, eight hundred fifty-five million, six hundred sixteen thousand, twenty".