638611554781 has 12 divisors (see below), whose sum is σ = 654704463420. Its totient is φ = 622851081600.

The previous prime is 638611554773. The next prime is 638611554829. The reversal of 638611554781 is 187455116836.

It can be written as a sum of positive squares in 2 ways, for example, as 611666332281 + 26945222500 = 782091^2 + 164150^2 .

It is not a de Polignac number, because 638611554781 - 2³ = 638611554773 is a prime.

It is a super-2 number, since 2×638611554781² (a number of 24 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (638611557781) 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, 250876 + ... + 1157653.

It is an arithmetic number, because the mean of its divisors is an integer number (54558705285).

Almost surely, 2^638611554781 is an apocalyptic number.

It is an amenable number.

638611554781 is a deficient number, since it is larger than the sum of its proper divisors (16092908639).

638611554781 is a wasteful number, since it uses less digits than its factorization.

638611554781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1408764 (or 1408697 counting only the distinct ones).

The product of its digits is 4838400, while the sum is 55.

The spelling of 638611554781 in words is "six hundred thirty-eight billion, six hundred eleven million, five hundred fifty-four thousand, seven hundred eighty-one".