21544061509 has 2 divisors, whose sum is σ = 21544061510. Its totient is φ = 21544061508.

The previous prime is 21544061507. The next prime is 21544061593. The reversal of 21544061509 is 90516044512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13062204100 + 8481857409 = 114290^2 + 92097^2 .

It is a cyclic number.

It is not a de Polignac number, because 21544061509 - 2¹ = 21544061507 is a prime.

Together with 21544061507, 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 (21544061507) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10772030754 + 10772030755.

It is an arithmetic number, because the mean of its divisors is an integer number (10772030755).

Almost surely, 2^21544061509 is an apocalyptic number.

It is an amenable number.

21544061509 is a deficient number, since it is larger than the sum of its proper divisors (1).

21544061509 is an equidigital number, since it uses as much as digits as its factorization.

21544061509 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 43200, while the sum is 37.

The spelling of 21544061509 in words is "twenty-one billion, five hundred forty-four million, sixty-one thousand, five hundred nine".