21556471391 has 16 divisors (see below), whose sum is σ = 26624822784. Its totient is φ = 16995381984.

The previous prime is 21556471367. The next prime is 21556471403. The reversal of 21556471391 is 19317465512.

It is not a de Polignac number, because 21556471391 - 2¹⁴ = 21556455007 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21556471331) by changing a digit.

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 15 ways as a sum of consecutive naturals, for example, 392771 + ... + 444276.

It is an arithmetic number, because the mean of its divisors is an integer number (1664051424).

Almost surely, 2^21556471391 is an apocalyptic number.

21556471391 is a deficient number, since it is larger than the sum of its proper divisors (5068351393).

21556471391 is a wasteful number, since it uses less digits than its factorization.

21556471391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 837350.

The product of its digits is 226800, while the sum is 44.

The spelling of 21556471391 in words is "twenty-one billion, five hundred fifty-six million, four hundred seventy-one thousand, three hundred ninety-one".