21973206978 has 18 divisors (see below), whose sum is σ = 47609977779. Its totient is φ = 7324192692.

The previous prime is 21973206949. The next prime is 21973206991. The reversal of 21973206978 is 87960237912.

21973206978 is a `hidden beast` number, since 2 + 197 + 320 + 69 + 78 = 666.

It can be written as a sum of positive squares in only one way, i.e., 10986603489 + 10986603489 = 104817^2 + 104817^2 .

It is a tau number, because it is divible by the number of its divisors (18).

It is an ABA number since it can be written as A⋅B^A, here for A=2, B=104817.

It is a Curzon number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 611433 + ... + 646371.

Almost surely, 2^21973206978 is an apocalyptic number.

21973206978 is an abundant number, since it is smaller than the sum of its proper divisors (25636770801).

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

21973206978 is an frugal number, since it uses more digits than its factorization.

21973206978 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 69886 (or 34944 counting only the distinct ones).

The product of its (nonzero) digits is 2286144, while the sum is 54.

The spelling of 21973206978 in words is "twenty-one billion, nine hundred seventy-three million, two hundred six thousand, nine hundred seventy-eight".