21555660720 has 320 divisors, whose sum is σ = 76603097088. Its totient is φ = 4963200000.

The previous prime is 21555660701. The next prime is 21555660727. The reversal of 21555660720 is 2706655512.

It is not an unprimeable number, because it can be changed into a prime (21555660727) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 9167545 + ... + 9169895.

Almost surely, 2^21555660720 is an apocalyptic number.

21555660720 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 21555660720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38301548544).

21555660720 is an abundant number, since it is smaller than the sum of its proper divisors (55047436368).

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

21555660720 is a wasteful number, since it uses less digits than its factorization.

21555660720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2552 (or 2546 counting only the distinct ones).

The product of its (nonzero) digits is 126000, while the sum is 39.

The spelling of 21555660720 in words is "twenty-one billion, five hundred fifty-five million, six hundred sixty thousand, seven hundred twenty".