21878168781 has 16 divisors (see below), whose sum is σ = 33426137600. Its totient is φ = 12468819888.

The previous prime is 21878168779. The next prime is 21878168801. The reversal of 21878168781 is 18786187812.

It is a happy number.

It is not a de Polignac number, because 21878168781 - 2¹ = 21878168779 is a prime.

It is a super-2 number, since 2×21878168781² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21878168771) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1366471 + ... + 1382388.

It is an arithmetic number, because the mean of its divisors is an integer number (2089133600).

Almost surely, 2^21878168781 is an apocalyptic number.

21878168781 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21878168781 is a deficient number, since it is larger than the sum of its proper divisors (11547968819).

21878168781 is a wasteful number, since it uses less digits than its factorization.

21878168781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2749248.

The product of its digits is 2408448, while the sum is 57.

The spelling of 21878168781 in words is "twenty-one billion, eight hundred seventy-eight million, one hundred sixty-eight thousand, seven hundred eighty-one".