21006689978 has 16 divisors (see below), whose sum is σ = 33171303840. Its totient is φ = 9949683600.

The previous prime is 21006689971. The next prime is 21006689989. The reversal of 21006689978 is 87998660012.

It is not an unprimeable number, because it can be changed into a prime (21006689971) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 769808 + ... + 796628.

It is an arithmetic number, because the mean of its divisors is an integer number (2073206490).

Almost surely, 2^21006689978 is an apocalyptic number.

21006689978 is a deficient number, since it is larger than the sum of its proper divisors (12164613862).

21006689978 is a wasteful number, since it uses less digits than its factorization.

21006689978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 47453.

The product of its (nonzero) digits is 2612736, while the sum is 56.

The spelling of 21006689978 in words is "twenty-one billion, six million, six hundred eighty-nine thousand, nine hundred seventy-eight".