21051287 has 16 divisors (see below), whose sum is σ = 22954752. Its totient is φ = 19232640.

The previous prime is 21051271. The next prime is 21051311. The reversal of 21051287 is 78215012.

It is a cyclic number.

It is not a de Polignac number, because 21051287 - 2⁴ = 21051271 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21051257) 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 15 ways as a sum of consecutive naturals, for example, 129068 + ... + 129230.

It is an arithmetic number, because the mean of its divisors is an integer number (1434672).

Almost surely, 2^21051287 is an apocalyptic number.

21051287 is a deficient number, since it is larger than the sum of its proper divisors (1903465).

21051287 is a wasteful number, since it uses less digits than its factorization.

21051287 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 358.

The product of its (nonzero) digits is 1120, while the sum is 26.

The square root of 21051287 is about 4588.1681529778. The cubic root of 21051287 is about 276.1168333691.

Adding to 21051287 its reverse (78215012), we get a palindrome (99266299).

The spelling of 21051287 in words is "twenty-one million, fifty-one thousand, two hundred eighty-seven".