1638683561 has 2 divisors, whose sum is σ = 1638683562. Its totient is φ = 1638683560.

The previous prime is 1638683549. The next prime is 1638683573. The reversal of 1638683561 is 1653868361.

It is a balanced prime because it is at equal distance from previous prime (1638683549) and next prime (1638683573).

It can be written as a sum of positive squares in only one way, i.e., 990675625 + 648007936 = 31475^2 + 25456^2 .

It is an emirp because it is prime and its reverse (1653868361) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1638683561 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (1638683581) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 819341780 + 819341781.

It is an arithmetic number, because the mean of its divisors is an integer number (819341781).

Almost surely, 2^1638683561 is an apocalyptic number.

1638683561 is the 18104-th centered decagonal number.

It is an amenable number.

1638683561 is a deficient number, since it is larger than the sum of its proper divisors (1).

1638683561 is an equidigital number, since it uses as much as digits as its factorization.

1638683561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 622080, while the sum is 47.

The square root of 1638683561 is about 40480.6566275795. The cubic root of 1638683561 is about 1178.9580865568.

The spelling of 1638683561 in words is "one billion, six hundred thirty-eight million, six hundred eighty-three thousand, five hundred sixty-one".