21878081820 has 72 divisors (see below), whose sum is σ = 75844021344. Its totient is φ = 5000704128.

The previous prime is 21878081789. The next prime is 21878081837. The reversal of 21878081820 is 2818087812.

It is a super-2 number, since 2×21878081820² (a number of 21 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 8680519 + ... + 8683038.

Almost surely, 2^21878081820 is an apocalyptic number.

21878081820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21878081820 is an abundant number, since it is smaller than the sum of its proper divisors (53965939524).

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

21878081820 is a wasteful number, since it uses less digits than its factorization.

21878081820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17363579 (or 17363574 counting only the distinct ones).

The product of its (nonzero) digits is 114688, while the sum is 45.

The spelling of 21878081820 in words is "twenty-one billion, eight hundred seventy-eight million, eighty-one thousand, eight hundred twenty".