> For example a(10) = 115 (one hundred and fifteen), and with this letters > we can make the name of ten numbers lesser than 150 : > 1 ONE, 3 THREE, 4 FOUR, 9 NINE, 10 TEN, 14 FOURTEEN, 15 FIFTEEN, 40 FORTY, > 49 FORTY NINE, 50 FIFTY, 51 FIFTY ONE, 90 NINETY, 94 NINETY FOUR and 100 > ONE HUNDRED From where comes the Y in 40, 49, 50, 51, 90, 94 ?