1638412721 has 6 divisors (see below), whose sum is σ = 1800900066. Its totient is φ = 1489466000.

The previous prime is 1638412717. The next prime is 1638412747. The reversal of 1638412721 is 1272148361.

It can be written as a sum of positive squares in only one way, i.e., 1550784400 + 87628321 = 39380^2 + 9361^2 .

It is not a de Polignac number, because 1638412721 - 2² = 1638412717 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1638412771) 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 in 5 ways as a sum of consecutive naturals, for example, 6770180 + ... + 6770421.

It is an arithmetic number, because the mean of its divisors is an integer number (300150011).

Almost surely, 2^1638412721 is an apocalyptic number.

1638412721 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

1638412721 is a deficient number, since it is larger than the sum of its proper divisors (162487345).

1638412721 is a wasteful number, since it uses less digits than its factorization.

1638412721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13540623 (or 13540612 counting only the distinct ones).

The product of its digits is 16128, while the sum is 35.

The square root of 1638412721 is about 40477.3111878741. The cubic root of 1638412721 is about 1178.8931306355.

The spelling of 1638412721 in words is "one billion, six hundred thirty-eight million, four hundred twelve thousand, seven hundred twenty-one".