636666642 has 40 divisors (see below), whose sum is σ = 1434914316. Its totient is φ = 210986208.

The previous prime is 636666637. The next prime is 636666647. The reversal of 636666642 is 246666636.

It is an interprime number because it is at equal distance from previous prime (636666637) and next prime (636666647).

It can be written as a sum of positive squares in 2 ways, for example, as 621056241 + 15610401 = 24921^2 + 3951^2 .

It is not an unprimeable number, because it can be changed into a prime (636666647) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 16668 + ... + 39384.

Almost surely, 2^636666642 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 636666642, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (717457158).

636666642 is an abundant number, since it is smaller than the sum of its proper divisors (798247674).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

636666642 is a wasteful number, since it uses less digits than its factorization.

636666642 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22904 (or 22895 counting only the distinct ones).

The product of its digits is 1119744, while the sum is 45.

The square root of 636666642 is about 25232.2540015750. The cubic root of 636666642 is about 860.2751247024.

The spelling of 636666642 in words is "six hundred thirty-six million, six hundred sixty-six thousand, six hundred forty-two".