21009409549 has 2 divisors, whose sum is σ = 21009409550. Its totient is φ = 21009409548.

The previous prime is 21009409541. The next prime is 21009409583. The reversal of 21009409549 is 94590490012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20339893924 + 669515625 = 142618^2 + 25875^2 .

It is a cyclic number.

It is not a de Polignac number, because 21009409549 - 2³ = 21009409541 is a prime.

It is a super-2 number, since 2×21009409549² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21009409541) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10504704774 + 10504704775.

It is an arithmetic number, because the mean of its divisors is an integer number (10504704775).

Almost surely, 2^21009409549 is an apocalyptic number.

It is an amenable number.

21009409549 is a deficient number, since it is larger than the sum of its proper divisors (1).

21009409549 is an equidigital number, since it uses as much as digits as its factorization.

21009409549 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 116640, while the sum is 43.

The spelling of 21009409549 in words is "twenty-one billion, nine million, four hundred nine thousand, five hundred forty-nine".