21087819 has 12 divisors (see below), whose sum is σ = 31108896. Its totient is φ = 13759152.

The previous prime is 21087809. The next prime is 21087827. The reversal of 21087819 is 91878012.

It is not a de Polignac number, because 21087819 - 2⁷ = 21087691 is a prime.

It is a super-2 number, since 2×21087819² = 889392220353522, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21087809) 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 in 11 ways as a sum of consecutive naturals, for example, 24504 + ... + 25349.

It is an arithmetic number, because the mean of its divisors is an integer number (2592408).

Almost surely, 2^21087819 is an apocalyptic number.

21087819 is a deficient number, since it is larger than the sum of its proper divisors (10021077).

21087819 is a wasteful number, since it uses less digits than its factorization.

21087819 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 49906 (or 49903 counting only the distinct ones).

The product of its (nonzero) digits is 8064, while the sum is 36.

The square root of 21087819 is about 4592.1475368285. The cubic root of 21087819 is about 276.2764636851.

The spelling of 21087819 in words is "twenty-one million, eighty-seven thousand, eight hundred nineteen".