This isn't that surprising. Lee Hsien Loong studied at Trinity College, Cambridge, where he was Senior Wrangler, and graduated with a first class honours in mathematics and a Diploma in Computer Science (with distinction).
I edited the wikipedia entry to include that even a prime minister was Senior Wrangler not only leading mathematicians and physicists. Good career prospects.
I can only think of recently killed Russian opposition politician Boris Nemtsov with similar mathematical achievements.
Angela Merkel (Kasner) also won a mathematics price during her physics doctorate studies, before she elected to work in agitprop and most likely as master stasi spy under the codenames ANITA and Black Widow.
Which brings me to the theory that being a spy will help you more getting to a prime minister job (Putin, Merkel), than being an excellent mathematician.
He's mentioned in the past that he briefly considered a career in academia (Mathematics). That didn't happen, of course. (source: http://www.moe.gov.sg/media/speeches/2003/sp20030603.htm)