21511244509 has 2 divisors, whose sum is σ = 21511244510. Its totient is φ = 21511244508.

The previous prime is 21511244507. The next prime is 21511244563. The reversal of 21511244509 is 90544211512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20227097284 + 1284147225 = 142222^2 + 35835^2 .

It is a cyclic number.

It is not a de Polignac number, because 21511244509 - 2¹ = 21511244507 is a prime.

Together with 21511244507, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21511244507) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10755622254 + 10755622255.

It is an arithmetic number, because the mean of its divisors is an integer number (10755622255).

Almost surely, 2^21511244509 is an apocalyptic number.

It is an amenable number.

21511244509 is a deficient number, since it is larger than the sum of its proper divisors (1).

21511244509 is an equidigital number, since it uses as much as digits as its factorization.

21511244509 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 14400, while the sum is 34.

The spelling of 21511244509 in words is "twenty-one billion, five hundred eleven million, two hundred forty-four thousand, five hundred nine".