21112561 has 2 divisors, whose sum is σ = 21112562. Its totient is φ = 21112560.

The previous prime is 21112547. The next prime is 21112601. The reversal of 21112561 is 16521112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20976400 + 136161 = 4580^2 + 369^2 .

It is a cyclic number.

It is not a de Polignac number, because 21112561 - 2⁷ = 21112433 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21112061) 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, 10556280 + 10556281.

It is an arithmetic number, because the mean of its divisors is an integer number (10556281).

Almost surely, 2^21112561 is an apocalyptic number.

It is an amenable number.

21112561 is a deficient number, since it is larger than the sum of its proper divisors (1).

21112561 is an equidigital number, since it uses as much as digits as its factorization.

21112561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 120, while the sum is 19.

The square root of 21112561 is about 4594.8406936476. The cubic root of 21112561 is about 276.3844717035.

Adding to 21112561 its reverse (16521112), we get a palindrome (37633673).

The spelling of 21112561 in words is "twenty-one million, one hundred twelve thousand, five hundred sixty-one".