21281247 has 12 divisors (see below), whose sum is σ = 33104344. Its totient is φ = 13096080.

The previous prime is 21281243. The next prime is 21281251. The reversal of 21281247 is 74218212.

It is an interprime number because it is at equal distance from previous prime (21281243) and next prime (21281251).

It is not a de Polignac number, because 21281247 - 2² = 21281243 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21281247.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21281243) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 90829 + ... + 91062.

Almost surely, 2^21281247 is an apocalyptic number.

21281247 is a deficient number, since it is larger than the sum of its proper divisors (11823097).

21281247 is a wasteful number, since it uses less digits than its factorization.

21281247 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 181910 (or 181907 counting only the distinct ones).

The product of its digits is 1792, while the sum is 27.

The square root of 21281247 is about 4613.1601966548. The cubic root of 21281247 is about 277.1186092512.

Adding to 21281247 its reverse (74218212), we get a palindrome (95499459).

It can be divided in two parts, 21281 and 247, that added together give a triangular number (21528 = T₂₀₇).

The spelling of 21281247 in words is "twenty-one million, two hundred eighty-one thousand, two hundred forty-seven".