21681247 has 8 divisors (see below), whose sum is σ = 24846336. Its totient is φ = 18533112.

The previous prime is 21681221. The next prime is 21681269. The reversal of 21681247 is 74218612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21681247 - 2²³ = 13292639 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 (21681217) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1363 + ... + 6724.

It is an arithmetic number, because the mean of its divisors is an integer number (3105792).

Almost surely, 2^21681247 is an apocalyptic number.

21681247 is a deficient number, since it is larger than the sum of its proper divisors (3165089).

21681247 is an equidigital number, since it uses as much as digits as its factorization.

21681247 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8477.

The product of its digits is 5376, while the sum is 31.

The square root of 21681247 is about 4656.3125968947. The cubic root of 21681247 is about 278.8440738336.

Adding to 21681247 its reverse (74218612), we get a palindrome (95899859).

The spelling of 21681247 in words is "twenty-one million, six hundred eighty-one thousand, two hundred forty-seven".