21561223 has 2 divisors, whose sum is σ = 21561224. Its totient is φ = 21561222.

The previous prime is 21561193. The next prime is 21561251. The reversal of 21561223 is 32216512.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21561223 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21561194 and 21561203.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21061223) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10780611 + 10780612.

It is an arithmetic number, because the mean of its divisors is an integer number (10780612).

Almost surely, 2^21561223 is an apocalyptic number.

21561223 is a deficient number, since it is larger than the sum of its proper divisors (1).

21561223 is an equidigital number, since it uses as much as digits as its factorization.

21561223 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 720, while the sum is 22.

The square root of 21561223 is about 4643.4064004780. The cubic root of 21561223 is about 278.3285756614.

Adding to 21561223 its reverse (32216512), we get a palindrome (53777735).

The spelling of 21561223 in words is "twenty-one million, five hundred sixty-one thousand, two hundred twenty-three".