21891118987 has 4 divisors (see below), whose sum is σ = 21892880416. Its totient is φ = 21889357560.

The previous prime is 21891118967. The next prime is 21891119069. The reversal of 21891118987 is 78981119812.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21891118987 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21891118967) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 861939 + ... + 886972.

It is an arithmetic number, because the mean of its divisors is an integer number (5473220104).

Almost surely, 2^21891118987 is an apocalyptic number.

21891118987 is a deficient number, since it is larger than the sum of its proper divisors (1761429).

21891118987 is a wasteful number, since it uses less digits than its factorization.

21891118987 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1761428.

The product of its digits is 580608, while the sum is 55.

The spelling of 21891118987 in words is "twenty-one billion, eight hundred ninety-one million, one hundred eighteen thousand, nine hundred eighty-seven".