1665448721 has 2 divisors, whose sum is σ = 1665448722. Its totient is φ = 1665448720.

The previous prime is 1665448717. The next prime is 1665448777. The reversal of 1665448721 is 1278445661.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1659421696 + 6027025 = 40736^2 + 2455^2 .

It is a cyclic number.

It is not a de Polignac number, because 1665448721 - 2² = 1665448717 is a prime.

It is not a weakly prime, because it can be changed into another prime (1665448121) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 832724360 + 832724361.

It is an arithmetic number, because the mean of its divisors is an integer number (832724361).

Almost surely, 2^1665448721 is an apocalyptic number.

It is an amenable number.

1665448721 is a deficient number, since it is larger than the sum of its proper divisors (1).

1665448721 is an equidigital number, since it uses as much as digits as its factorization.

1665448721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 322560, while the sum is 44.

The square root of 1665448721 is about 40809.9095931368. The cubic root of 1665448721 is about 1185.3422242654.

The spelling of 1665448721 in words is "one billion, six hundred sixty-five million, four hundred forty-eight thousand, seven hundred twenty-one".