21138287 has 4 divisors (see below), whose sum is σ = 21164856. Its totient is φ = 21111720.

The previous prime is 21138281. The next prime is 21138307. The reversal of 21138287 is 78283112.

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

It is a cyclic number.

It is not a de Polignac number, because 21138287 - 2⁶ = 21138223 is a prime.

It is a super-3 number, since 3×21138287³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21138281) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 12053 + ... + 13694.

It is an arithmetic number, because the mean of its divisors is an integer number (5291214).

Almost surely, 2^21138287 is an apocalyptic number.

21138287 is a deficient number, since it is larger than the sum of its proper divisors (26569).

21138287 is an equidigital number, since it uses as much as digits as its factorization.

21138287 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26568.

The product of its digits is 5376, while the sum is 32.

The square root of 21138287 is about 4597.6392855464. The cubic root of 21138287 is about 276.4966858001.

It can be divided in two parts, 21138 and 287, that multiplied together give a palindrome (6066606).

The spelling of 21138287 in words is "twenty-one million, one hundred thirty-eight thousand, two hundred eighty-seven".