21000099978 has 48 divisors (see below), whose sum is σ = 53454806496. Its totient is φ = 5874153120.

The previous prime is 21000099973. The next prime is 21000099997. The reversal of 21000099978 is 87999000012.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21000099973) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 4076700 + ... + 4081847.

It is an arithmetic number, because the mean of its divisors is an integer number (1113641802).

Almost surely, 2^21000099978 is an apocalyptic number.

21000099978 is an abundant number, since it is smaller than the sum of its proper divisors (32454706518).

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

21000099978 is a wasteful number, since it uses less digits than its factorization.

21000099978 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8158579 (or 8158576 counting only the distinct ones).

The product of its (nonzero) digits is 81648, while the sum is 45.

The spelling of 21000099978 in words is "twenty-one billion, ninety-nine thousand, nine hundred seventy-eight".