21227561 has 2 divisors, whose sum is σ = 21227562. Its totient is φ = 21227560.

The previous prime is 21227533. The next prime is 21227567. The reversal of 21227561 is 16572212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11424400 + 9803161 = 3380^2 + 3131^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21227561 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21227561.

It is not a weakly prime, because it can be changed into another prime (21227567) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10613780 + 10613781.

It is an arithmetic number, because the mean of its divisors is an integer number (10613781).

Almost surely, 2^21227561 is an apocalyptic number.

It is an amenable number.

21227561 is a deficient number, since it is larger than the sum of its proper divisors (1).

21227561 is an equidigital number, since it uses as much as digits as its factorization.

21227561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1680, while the sum is 26.

The square root of 21227561 is about 4607.3377345274. The cubic root of 21227561 is about 276.8853848609.

Adding to 21227561 its reverse (16572212), we get a palindrome (37799773).

The spelling of 21227561 in words is "twenty-one million, two hundred twenty-seven thousand, five hundred sixty-one".