1639991997 has 12 divisors (see below), whose sum is σ = 2707288480. Its totient is φ = 937138248.

The previous prime is 1639991987. The next prime is 1639991999. The reversal of 1639991997 is 7991999361.

It is not a de Polignac number, because 1639991997 - 2⁶ = 1639991933 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (63), and also a Moran number because the ratio is a prime number: 26031619 = 1639991997 / (1 + 6 + 3 + 9 + 9 + 9 + 1 + 9 + 9 + 7).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1639991999) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 13015747 + ... + 13015872.

Almost surely, 2^1639991997 is an apocalyptic number.

It is an amenable number.

1639991997 is a deficient number, since it is larger than the sum of its proper divisors (1067296483).

1639991997 is a wasteful number, since it uses less digits than its factorization.

1639991997 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 26031632 (or 26031629 counting only the distinct ones).

The product of its digits is 7440174, while the sum is 63.

The square root of 1639991997 is about 40496.8146525131. The cubic root of 1639991997 is about 1179.2717897537.

The spelling of 1639991997 in words is "one billion, six hundred thirty-nine million, nine hundred ninety-one thousand, nine hundred ninety-seven".