21216361 has 2 divisors, whose sum is σ = 21216362. Its totient is φ = 21216360.

The previous prime is 21216263. The next prime is 21216389. The reversal of 21216361 is 16361212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11256025 + 9960336 = 3355^2 + 3156^2 .

It is a cyclic number.

It is not a de Polignac number, because 21216361 - 2¹⁷ = 21085289 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is not a weakly prime, because it can be changed into another prime (21216061) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10608180 + 10608181.

It is an arithmetic number, because the mean of its divisors is an integer number (10608181).

Almost surely, 2^21216361 is an apocalyptic number.

It is an amenable number.

21216361 is a deficient number, since it is larger than the sum of its proper divisors (1).

21216361 is an equidigital number, since it uses as much as digits as its factorization.

21216361 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 432, while the sum is 22.

The square root of 21216361 is about 4606.1221216985. The cubic root of 21216361 is about 276.8366799112.

Adding to 21216361 its reverse (16361212), we get a palindrome (37577573).

The spelling of 21216361 in words is "twenty-one million, two hundred sixteen thousand, three hundred sixty-one".