21109587891 has 16 divisors (see below), whose sum is σ = 32300471808. Its totient is φ = 12012566400.

The previous prime is 21109587853. The next prime is 21109587923. The reversal of 21109587891 is 19878590112.

It is not a de Polignac number, because 21109587891 - 2¹⁰ = 21109586867 is a prime.

It is a super-2 number, since 2×21109587891² (a number of 21 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21109582891) 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, 2080455 + ... + 2090576.

It is an arithmetic number, because the mean of its divisors is an integer number (2018779488).

Almost surely, 2^21109587891 is an apocalyptic number.

21109587891 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21109587891 is a deficient number, since it is larger than the sum of its proper divisors (11190883917).

21109587891 is a wasteful number, since it uses less digits than its factorization.

21109587891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4171282.

The product of its (nonzero) digits is 362880, while the sum is 51.

The spelling of 21109587891 in words is "twenty-one billion, one hundred nine million, five hundred eighty-seven thousand, eight hundred ninety-one".