21100121019978 has 384 divisors, whose sum is σ = 62399676616704. Its totient is φ = 4584319027200.

The previous prime is 21100121019977. The next prime is 21100121020037. The reversal of 21100121019978 is 87991012100112.

It is a Harshad number since it is a multiple of its sum of digits (42).

It is not an unprimeable number, because it can be changed into a prime (21100121019977) by changing a digit.

It is a polite number, since it can be written in 191 ways as a sum of consecutive naturals, for example, 49656258 + ... + 50079378.

It is an arithmetic number, because the mean of its divisors is an integer number (162499157856).

Almost surely, 2^{21100121019978} is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21100121019978, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31199838308352).

21100121019978 is an abundant number, since it is smaller than the sum of its proper divisors (41299555596726).

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

21100121019978 is a wasteful number, since it uses less digits than its factorization.

21100121019978 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 423218 (or 423199 counting only the distinct ones).

The product of its (nonzero) digits is 18144, while the sum is 42.

The spelling of 21100121019978 in words is "twenty-one trillion, one hundred billion, one hundred twenty-one million, nineteen thousand, nine hundred seventy-eight".