21556049991 has 8 divisors (see below), whose sum is σ = 32847314304. Its totient is φ = 12317742840.

The previous prime is 21556049987. The next prime is 21556050007. The reversal of 21556049991 is 19994065512.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21556049991 - 2² = 21556049987 is a prime.

It is a super-2 number, since 2×21556049991² (a number of 21 digits) contains 22 as substring.

It is a Smith number, since the sum of its digits (51) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21556048991) 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, 513239265 + ... + 513239306.

It is an arithmetic number, because the mean of its divisors is an integer number (4105914288).

Almost surely, 2^21556049991 is an apocalyptic number.

21556049991 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21556049991 is a deficient number, since it is larger than the sum of its proper divisors (11291264313).

21556049991 is a wasteful number, since it uses less digits than its factorization.

21556049991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1026478581.

The product of its (nonzero) digits is 874800, while the sum is 51.

The spelling of 21556049991 in words is "twenty-one billion, five hundred fifty-six million, forty-nine thousand, nine hundred ninety-one".