21556247 has 2 divisors, whose sum is σ = 21556248. Its totient is φ = 21556246.

The previous prime is 21556231. The next prime is 21556273. The reversal of 21556247 is 74265512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21556247 - 2⁴ = 21556231 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21556547) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10778123 + 10778124.

It is an arithmetic number, because the mean of its divisors is an integer number (10778124).

Almost surely, 2^21556247 is an apocalyptic number.

21556247 is a deficient number, since it is larger than the sum of its proper divisors (1).

21556247 is an equidigital number, since it uses as much as digits as its factorization.

21556247 is an evil number, because the sum of its binary digits is even.

The product of its digits is 16800, while the sum is 32.

The square root of 21556247 is about 4642.8705560246. The cubic root of 21556247 is about 278.3071626901.

The spelling of 21556247 in words is "twenty-one million, five hundred fifty-six thousand, two hundred forty-seven".