Write a mathematical function whose result is "hello world"
I'll do better than just printing it, I'll print it infinitely many times!

The rational number

1767707668033969 / 3656158440062975


returns the following base-36 expansion:

0.helloworldhelloworldhelloworldhelloworldhelloworld...


Try it out! (Wolfram Alpha)

Or, if you want a more subliminal message, try:

2399843759207982499621172523113947162810942763812298565948669
/ 1357602166130257152481187563160405662935023615


Which returns (again in base 36):

helloworld.helpimtrappedinanumberfactoryhelpimtrappedinanumberfactoryhelpimtrappedinanumberfactory...


If your program worked with only integers, you'd never see the fractional part.