1965721809 has 16 divisors (see below), whose sum is σ = 2639673152. Its totient is φ = 1301142528.

The previous prime is 1965721799. The next prime is 1965721831. The reversal of 1965721809 is 9081275691.

It is not a de Polignac number, because 1965721809 - 2¹⁵ = 1965689041 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1965721859) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 973569 + ... + 975585.

It is an arithmetic number, because the mean of its divisors is an integer number (164979572).

Almost surely, 2^1965721809 is an apocalyptic number.

It is an amenable number.

1965721809 is a deficient number, since it is larger than the sum of its proper divisors (673951343).

1965721809 is a wasteful number, since it uses less digits than its factorization.

1965721809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4176.

The product of its (nonzero) digits is 272160, while the sum is 48.

The square root of 1965721809 is about 44336.4613946580. The cubic root of 1965721809 is about 1252.6815625177.

The spelling of 1965721809 in words is "one billion, nine hundred sixty-five million, seven hundred twenty-one thousand, eight hundred nine".