6399945521 has 2 divisors, whose sum is σ = 6399945522. Its totient is φ = 6399945520.

The previous prime is 6399945499. The next prime is 6399945529. The reversal of 6399945521 is 1255499936.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 6390403600 + 9541921 = 79940^2 + 3089^2 .

It is a cyclic number.

It is not a de Polignac number, because 6399945521 - 2¹⁰ = 6399944497 is a prime.

It is a super-2 number, since 2×6399945521² = 81918605343535922882, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (6399945529) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3199972760 + 3199972761.

It is an arithmetic number, because the mean of its divisors is an integer number (3199972761).

Almost surely, 2^6399945521 is an apocalyptic number.

It is an amenable number.

6399945521 is a deficient number, since it is larger than the sum of its proper divisors (1).

6399945521 is an equidigital number, since it uses as much as digits as its factorization.

6399945521 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2624400, while the sum is 53.

The square root of 6399945521 is about 79999.6595055254. The cubic root of 6399945521 is about 1856.6302653235.

The spelling of 6399945521 in words is "six billion, three hundred ninety-nine million, nine hundred forty-five thousand, five hundred twenty-one".