21561011 has 2 divisors, whose sum is σ = 21561012. Its totient is φ = 21561010.

The previous prime is 21560989. The next prime is 21561013. The reversal of 21561011 is 11016512.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21561011 is a prime.

Together with 21561013, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21561013) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10780505 + 10780506.

It is an arithmetic number, because the mean of its divisors is an integer number (10780506).

Almost surely, 2^21561011 is an apocalyptic number.

21561011 is a deficient number, since it is larger than the sum of its proper divisors (1).

21561011 is an equidigital number, since it uses as much as digits as its factorization.

21561011 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 60, while the sum is 17.

The square root of 21561011 is about 4643.3835723532. The cubic root of 21561011 is about 278.3276634396.

Adding to 21561011 its reverse (11016512), we get a palindrome (32577523).

The spelling of 21561011 in words is "twenty-one million, five hundred sixty-one thousand, eleven".