Intuitively, I would guess it's 「いってんさ」, but I could image 「いちてんさ」just as well. For bonus points: is there any reference or dictionary that explains the pronunciation of numbers with counters ...
This recent question brought to mind a question of my own. The Japanese name for the Twenty-One Demands made by Japan in 1915 to the Republic of China is romanised on the wikipedia page as 対華二十一ヵ条要求 ...
What is the correct pronunciation for 1カ所 ? It means: 1 place Context: ユーティリティ関数として定義されているわりには1カ所からしか呼ばれていない。 It is defined as a utility function, but only called in one place.