5. Observe the array:
(1),(3,5),(7,9,11),(13,15,17,19), .....

In which group is 2003?
(Tip: Use the trial method. The first 45 groups have a total of $1+2+\cdots$ $+45=1035$ numbers. The last number of the 45th group is 2069, and the first number is 1981, so, 2003 is in the 45th group.)