1638861387 has 24 divisors (see below), whose sum is σ = 2378010096. Its totient is φ = 1000470528.

The previous prime is 1638861383. The next prime is 1638861391. The reversal of 1638861387 is 7831688361.

It is an interprime number because it is at equal distance from previous prime (1638861383) and next prime (1638861391).

It is not a de Polignac number, because 1638861387 - 2² = 1638861383 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (51).

It is not an unprimeable number, because it can be changed into a prime (1638861383) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 58083 + ... + 81555.

It is an arithmetic number, because the mean of its divisors is an integer number (99083754).

Almost surely, 2^1638861387 is an apocalyptic number.

1638861387 is a gapful number since it is divisible by the number (17) formed by its first and last digit.

1638861387 is a deficient number, since it is larger than the sum of its proper divisors (739148709).

1638861387 is a wasteful number, since it uses less digits than its factorization.

1638861387 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23567 (or 23530 counting only the distinct ones).

The product of its digits is 1161216, while the sum is 51.

The square root of 1638861387 is about 40482.8529997578. The cubic root of 1638861387 is about 1179.0007309132. Note that the first 3 decimals are identical.

The spelling of 1638861387 in words is "one billion, six hundred thirty-eight million, eight hundred sixty-one thousand, three hundred eighty-seven".