21416561 has 2 divisors, whose sum is σ = 21416562. Its totient is φ = 21416560.

The previous prime is 21416543. The next prime is 21416597. The reversal of 21416561 is 16561412.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21298225 + 118336 = 4615^2 + 344^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21416561 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

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

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 21416561.

It is not a weakly prime, because it can be changed into another prime (21416531) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10708280 + 10708281.

It is an arithmetic number, because the mean of its divisors is an integer number (10708281).

Almost surely, 2^21416561 is an apocalyptic number.

It is an amenable number.

21416561 is a deficient number, since it is larger than the sum of its proper divisors (1).

21416561 is an equidigital number, since it uses as much as digits as its factorization.

21416561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1440, while the sum is 26.

The square root of 21416561 is about 4627.8030424814. The cubic root of 21416561 is about 277.7047094866.

Adding to 21416561 its reverse (16561412), we get a palindrome (37977973).

The spelling of 21416561 in words is "twenty-one million, four hundred sixteen thousand, five hundred sixty-one".