21123021978 has 48 divisors (see below), whose sum is σ = 46922908032. Its totient is φ = 6863400000.

The previous prime is 21123021977. The next prime is 21123022007. The reversal of 21123021978 is 87912032112.

It is not an unprimeable number, because it can be changed into a prime (21123021971) 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 23 ways as a sum of consecutive naturals, for example, 896853 + ... + 920103.

It is an arithmetic number, because the mean of its divisors is an integer number (977560584).

Almost surely, 2^21123021978 is an apocalyptic number.

21123021978 is an abundant number, since it is smaller than the sum of its proper divisors (25799886054).

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

21123021978 is a wasteful number, since it uses less digits than its factorization.

21123021978 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 24531 (or 24528 counting only the distinct ones).

The product of its (nonzero) digits is 12096, while the sum is 36.

The spelling of 21123021978 in words is "twenty-one billion, one hundred twenty-three million, twenty-one thousand, nine hundred seventy-eight".