21000656666808 has 144 divisors (see below), whose sum is σ = 70386816586320. Its totient is φ = 5538634702848.

The previous prime is 21000656666797. The next prime is 21000656666861. The reversal of 21000656666808 is 80866665600012.

It is a happy number.

It is a congruent number.

It is an unprimeable number.

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 35 ways as a sum of consecutive naturals, for example, 123192841 + ... + 123363192.

It is an arithmetic number, because the mean of its divisors is an integer number (488797337405).

Almost surely, 2^{21000656666808} is an apocalyptic number.

21000656666808 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

21000656666808 is an abundant number, since it is smaller than the sum of its proper divisors (49386159919512).

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

21000656666808 is a wasteful number, since it uses less digits than its factorization.

21000656666808 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 246556078 (or 246556058 counting only the distinct ones).

The product of its (nonzero) digits is 4976640, while the sum is 54.

The spelling of 21000656666808 in words is "twenty-one trillion, six hundred fifty-six million, six hundred sixty-six thousand, eight hundred eight".