21012221199978 has 128 divisors (see below), whose sum is σ = 47412913766400. Its totient is φ = 6896796826176.

The previous prime is 21012221199941. The next prime is 21012221199979. The reversal of 21012221199978 is 87999112221012.

It is a happy number.

21012221199978 is a `hidden beast` number, since 210 + 1 + 222 + 119 + 9 + 97 + 8 = 666.

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

It is not an unprimeable number, because it can be changed into a prime (21012221199979) 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, 2899433551 + ... + 2899440797.

It is an arithmetic number, because the mean of its divisors is an integer number (370413388800).

Almost surely, 2^{21012221199978} is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21012221199978, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23706456883200).

21012221199978 is an abundant number, since it is smaller than the sum of its proper divisors (26400692566422).

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

21012221199978 is a wasteful number, since it uses less digits than its factorization.

21012221199978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9393 (or 9387 counting only the distinct ones).

The product of its (nonzero) digits is 653184, while the sum is 54.

The spelling of 21012221199978 in words is "twenty-one trillion, twelve billion, two hundred twenty-one million, one hundred ninety-nine thousand, nine hundred seventy-eight".