637688021 has 2 divisors, whose sum is σ = 637688022. Its totient is φ = 637688020.

The previous prime is 637687993. The next prime is 637688053. The reversal of 637688021 is 120886736.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 539400625 + 98287396 = 23225^2 + 9914^2 .

It is a cyclic number.

It is not a de Polignac number, because 637688021 - 2²⁶ = 570579157 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 637688021.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (637685021) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 318844010 + 318844011.

It is an arithmetic number, because the mean of its divisors is an integer number (318844011).

Almost surely, 2^637688021 is an apocalyptic number.

It is an amenable number.

637688021 is a deficient number, since it is larger than the sum of its proper divisors (1).

637688021 is an equidigital number, since it uses as much as digits as its factorization.

637688021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 96768, while the sum is 41.

The square root of 637688021 is about 25252.4854420312. The cubic root of 637688021 is about 860.7349139845.

The spelling of 637688021 in words is "six hundred thirty-seven million, six hundred eighty-eight thousand, twenty-one".