21561003311 has 2 divisors, whose sum is σ = 21561003312. Its totient is φ = 21561003310.

The previous prime is 21561003173. The next prime is 21561003319. The reversal of 21561003311 is 11330016512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21561003311 - 2³⁴ = 4381134127 is a prime.

It is a Sophie Germain prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21561003319) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10780501655 + 10780501656.

It is an arithmetic number, because the mean of its divisors is an integer number (10780501656).

Almost surely, 2^21561003311 is an apocalyptic number.

21561003311 is a deficient number, since it is larger than the sum of its proper divisors (1).

21561003311 is an equidigital number, since it uses as much as digits as its factorization.

21561003311 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 540, while the sum is 23.

Adding to 21561003311 its reverse (11330016512), we get a palindrome (32891019823).

The spelling of 21561003311 in words is "twenty-one billion, five hundred sixty-one million, three thousand, three hundred eleven".