The first obvious connection to mathematical concepts in Life of Pi would be in the title. Pi is widely used in measurement and, as an irrational number, one with an unending number of units after the decimal, it is not easily explained. Pi's first interpretation of his ordeal after the sinking of The Tsimtsum is considered so far-fetched by the authorities that it is rejected by them as not being a version of the truth. It is irrational! Pi himself is a very complex character.
The mathematical Pi is often rounded off to either 3.17 or 22/7 for ease of use - people prefer to use it. So too with the story. Even though, eventually the story of Richard Parker (the Bengal Tiger) may be preferred, it is at first rejected. Pi points out that "you risk throwing out the universe with the bathwater" when you restrict your understanding of something. When the symbol Pi is rounded-off, the answer is obviously restricted and useful only in approximations - so too the story. The Japanese who, at first had their own "approximations" of the truth about Pi's life on the boat, are restricted by their understanding of his ordeal.
There is far more to Pi, the boy, than meets the eye; and the symbol Pi is the same. The symbol has a scientific basis but cannot be expressed exactly and precisely. Pi,the boy spends his time trying to find the meaning of life and adopts more than one religion in his quest. He quotes Gandhi "all religions are true."
Pi, in mathematics and science is a constant and yet it defies constancy as its application is widespread; apparent in nature (the formation of a rainbow), giving it an almost philosophical edge, science (DNA structure) and the obvious statistical arena. Pi, the character, survives against all the odds, his own constancy but adaptability (paradox?) ensuring his safe return to civilization.
The mathematical conceptual connections may be quite abstract but this adds to the mysticism that surrounds Pi and all that he has come to stand for and the religion in which he believes. Religion may seem irrational to some people but it allows others to actually "find themselves." Religion itself has seeming contradictions but they do not make it less believable. Therefore, "which story do you prefer?" Mathematics is precise and yet Pi has hundreds of thousands of decimals, and, as yet is not fully computed. You can choose at which decimal you want to stop, justy like you can choose which story you prefer!