21997861578 has 320 divisors, whose sum is σ = 64008806400. Its totient is φ = 5479747200.

The previous prime is 21997861577. The next prime is 21997861601. The reversal of 21997861578 is 87516879912.

21997861578 is a `hidden beast` number, since 2 + 1 + 9 + 9 + 7 + 8 + 615 + 7 + 8 = 666.

It is a Harshad number since it is a multiple of its sum of digits (63).

It is not an unprimeable number, because it can be changed into a prime (21997861573) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 159 ways as a sum of consecutive naturals, for example, 63030948 + ... + 63031296.

It is an arithmetic number, because the mean of its divisors is an integer number (200027520).

Almost surely, 2^21997861578 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21997861578, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32004403200).

21997861578 is an abundant number, since it is smaller than the sum of its proper divisors (42010944822).

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

21997861578 is a wasteful number, since it uses less digits than its factorization.

21997861578 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 575 (or 566 counting only the distinct ones).

The product of its digits is 15240960, while the sum is 63.

The spelling of 21997861578 in words is "twenty-one billion, nine hundred ninety-seven million, eight hundred sixty-one thousand, five hundred seventy-eight".