final var partCount = 12;
var partSize = digits.length() / partCount;
var f = new StringBuilder(digits.length() + partCount);
for (var i = 0; i < partCount; i++) {
final var partCount = 12;
var partSize = digits.length() / partCount;
var f = new StringBuilder(digits.length() + partCount);
for (var i = 0; i < partCount; i++) {