21286251 has 24 divisors (see below), whose sum is σ = 36990720. Its totient is φ = 11522736.

The previous prime is 21286249. The next prime is 21286267. The reversal of 21286251 is 15268212.

It is a happy number.

It is not a de Polignac number, because 21286251 - 2¹ = 21286249 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21286241) 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 23 ways as a sum of consecutive naturals, for example, 7695 + ... + 10088.

It is an arithmetic number, because the mean of its divisors is an integer number (1541280).

Almost surely, 2^21286251 is an apocalyptic number.

21286251 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21286251 is a deficient number, since it is larger than the sum of its proper divisors (15704469).

21286251 is a wasteful number, since it uses less digits than its factorization.

21286251 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17815 (or 17812 counting only the distinct ones).

The product of its digits is 1920, while the sum is 27.

The square root of 21286251 is about 4613.7025261714. The cubic root of 21286251 is about 277.1403277912.

The spelling of 21286251 in words is "twenty-one million, two hundred eighty-six thousand, two hundred fifty-one".