638657731421 has 2 divisors, whose sum is σ = 638657731422. Its totient is φ = 638657731420.

The previous prime is 638657731417. The next prime is 638657731471. The reversal of 638657731421 is 124137756836.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 499263775396 + 139393956025 = 706586^2 + 373355^2 .

It is a cyclic number.

It is not a de Polignac number, because 638657731421 - 2² = 638657731417 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (638657731471) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 319328865710 + 319328865711.

It is an arithmetic number, because the mean of its divisors is an integer number (319328865711).

Almost surely, 2^638657731421 is an apocalyptic number.

It is an amenable number.

638657731421 is a deficient number, since it is larger than the sum of its proper divisors (1).

638657731421 is an equidigital number, since it uses as much as digits as its factorization.

638657731421 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5080320, while the sum is 53.

The spelling of 638657731421 in words is "six hundred thirty-eight billion, six hundred fifty-seven million, seven hundred thirty-one thousand, four hundred twenty-one".