21391851778 has 16 divisors (see below), whose sum is σ = 35008731360. Its totient is φ = 9722490400.

The previous prime is 21391851763. The next prime is 21391851779. The reversal of 21391851778 is 87715819312.

It is a super-2 number, since 2×21391851778² (a number of 21 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21391851779) 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, 169473 + ... + 267403.

It is an arithmetic number, because the mean of its divisors is an integer number (2188045710).

Almost surely, 2^21391851778 is an apocalyptic number.

21391851778 is a deficient number, since it is larger than the sum of its proper divisors (13616879582).

21391851778 is a wasteful number, since it uses less digits than its factorization.

21391851778 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 107873.

The product of its digits is 846720, while the sum is 52.

The spelling of 21391851778 in words is "twenty-one billion, three hundred ninety-one million, eight hundred fifty-one thousand, seven hundred seventy-eight".