638737861 has 2 divisors, whose sum is σ = 638737862. Its totient is φ = 638737860.

The previous prime is 638737859. The next prime is 638737903. The reversal of 638737861 is 168737836.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 479347236 + 159390625 = 21894^2 + 12625^2 .

It is a cyclic number.

It is not a de Polignac number, because 638737861 - 2¹ = 638737859 is a prime.

Together with 638737859, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (638737961) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 319368930 + 319368931.

It is an arithmetic number, because the mean of its divisors is an integer number (319368931).

Almost surely, 2^638737861 is an apocalyptic number.

It is an amenable number.

638737861 is a deficient number, since it is larger than the sum of its proper divisors (1).

638737861 is an equidigital number, since it uses as much as digits as its factorization.

638737861 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1016064, while the sum is 49.

The square root of 638737861 is about 25273.2637583673. The cubic root of 638737861 is about 861.2070040319.

The spelling of 638737861 in words is "six hundred thirty-eight million, seven hundred thirty-seven thousand, eight hundred sixty-one".