636739021 has 2 divisors, whose sum is σ = 636739022. Its totient is φ = 636739020.

The previous prime is 636739007. The next prime is 636739027. The reversal of 636739021 is 120937636.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 501132996 + 135606025 = 22386^2 + 11645^2 .

It is a cyclic number.

It is not a de Polignac number, because 636739021 - 2¹¹ = 636736973 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (636739027) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 318369510 + 318369511.

It is an arithmetic number, because the mean of its divisors is an integer number (318369511).

Almost surely, 2^636739021 is an apocalyptic number.

It is an amenable number.

636739021 is a deficient number, since it is larger than the sum of its proper divisors (1).

636739021 is an equidigital number, since it uses as much as digits as its factorization.

636739021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 40824, while the sum is 37.

The square root of 636739021 is about 25233.6882163508. The cubic root of 636739021 is about 860.3077233915.

The spelling of 636739021 in words is "six hundred thirty-six million, seven hundred thirty-nine thousand, twenty-one".