>>234 dart
https://ideone.com/e23wRv
void main() {
var rev = (n) => int.parse(n.toString().split('').reversed.join());
var f = (n) => Iterable.generate(n + 1).map((i) => [n - i, n + i].where((x) => x == rev(x))).firstWhere((a) => a.isNotEmpty).toSet().toList();
print([0, 17, 100].map((n) => [n, f(n)]));
}