(9) | Accounts receivable, net |
| | December 31, | | |||||||
| | 2017 | | 2016 | | 2015 | | |||
Trade receivables | | $ | 2,673,705 | | | 2,482,077 | | | 1,867,104 | |
Allowance for doubtful accounts | | | (96,900) | | | (97,400) | | | (81,641) | |
Other receivables | | | 22,403 | | | 140,265 | | | 76,787 | |
Government grant | | | - | | | - | | | 40 | |
Income tax receivable | | | 57,186 | | | 115,428 | | | 143,517 | |
Recoverable value-added tax and other recoverable taxes | | | 970,484 | | | 988,774 | | | 527,620 | |
| | $ | 3,626,878 | | | 3,629,144 | | | 2,533,427 | |
| | December 31, | | |||||||
| | 2017 | | 2016 | | 2015 | | |||
Past due 0 to 60 days | | | 200,413 | | | 164,458 | | | 129,315 | |
Past due by more than 60 days | | | 6,190 | | | 3,395 | | | 3,443 | |
| | $ | 206,603 | | | 167,853 | | | 132,758 | |
| | 2017 | | 2016 | | 2015 | | |||
Balance as of January 1 | | $ | (97,400) | | | (81,641) | | | (76,793) | |
Increase in allowance | | | (14,800) | | | (18,405) | | | (17,179) | |
Amounts written off | | | 15,287 | | | 2,818 | | | 12,454 | |
Currency translation effect | | | 13 | | | (172) | | | (123) | |
Balance as of December 31, | | $ | (96,900) | | | (97,400) | | | (81,641) | |