21109987 has 2 divisors, whose sum is σ = 21109988.
Its totient is φ = 21109986.
The previous prime is 21109973. The next prime is 21110027. The reversal of 21109987 is 78990112.
It is a weak prime.
It is a cyclic number.
It is a de Polignac number, because none of the positive numbers 2k-21109987 is a prime.
It is a super-2 number, since 2×211099872 = 891263102280338, which contains 22 as substring.
It is not a weakly prime, because it can be changed into another prime (21109927) by changing a digit.
It is a pernicious number, because its binary representation contains a prime number (11) of ones.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10554993 + 10554994.
It is an arithmetic number, because the mean of its divisors is an integer number (10554994).
Almost surely, 221109987 is an apocalyptic number.
21109987 is a deficient number, since it is larger than the sum of its proper divisors (1).
21109987 is an equidigital number, since it uses as much as digits as its factorization.
21109987 is an odious number, because the sum of its binary digits is odd.
The product of its (nonzero) digits is 9072, while the sum is 37.
The square root of 21109987 is about 4594.5605883479.
The cubic root of 21109987 is about 276.3732391716.
The spelling of 21109987 in words is "twenty-one million, one hundred nine thousand, nine hundred eighty-seven".