21804247 has 2 divisors, whose sum is σ = 21804248. Its totient is φ = 21804246.

The previous prime is 21804241. The next prime is 21804269. The reversal of 21804247 is 74240812.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21804247 - 2³ = 21804239 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21804241) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10902123 + 10902124.

It is an arithmetic number, because the mean of its divisors is an integer number (10902124).

Almost surely, 2^21804247 is an apocalyptic number.

21804247 is a deficient number, since it is larger than the sum of its proper divisors (1).

21804247 is an equidigital number, since it uses as much as digits as its factorization.

21804247 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3584, while the sum is 28.

The square root of 21804247 is about 4669.5017935536. The cubic root of 21804247 is about 279.3703837570.

It can be divided in two parts, 218042 and 47, that added together give a square (218089 = 467²).

The spelling of 21804247 in words is "twenty-one million, eight hundred four thousand, two hundred forty-seven".