Airbus aircraft start at cn 1 and go up in sequence.
There are 4 families of Airbus aircraft :
A300/A310 currently up to cn 863
A318/A319/A320/A321 currently up to cn 2550(ish)
A330/A340 currently up to cn 700(ish)
A380 not yet in service obviously
Boeing aircraft work differently. They have block numbers, line numbers and construction numbers. The block numbers are for Boeing maintenance record keeping and they comprise of two letters and three numbers, eg. YM522 will be B737-700 VH
-VBZ for Virgin Blue.
I'm not sure how the letters or numbers are allocated but basically all the Yx series belong to the 73NG's, Vx to the 767's, Nx to the 757's, Rx to the 747's, Wx to the 777's. The second letter seems to have something to do with the customer but several customers use the same letter. For example YJ is Continental, Ryanair, Qantas, COPA, Futura and some leasing companies. YK
belongs to another group and so it goes on.
The numbers following them tend to go up in sequence for each new aircraft. For example, Ryanair's EI
was YJ842, DHB YJ843, DHC YJ843, DHD YJ844 etc.
The line number is the sequence they come off the production line. Currently the 737's are at line 1780 (N222WN for Southwest). The 747's are at line 1363 (JA02KZ for Nippon Cargo). The 767's are at line 935 (JA613J for JAL). The 777's are at line 530 (F-GSQK for Air France).
The constructor number is different again and I have to admit this is where my knowledge ends as I don't understand the sequencing. I suspect it could be that when an airline places an order with Boeing they are immediately allocated the next number in the order book but I'm only guessing. This is a 5 digit number, for example B737-700 VH
-VBZ is block number YM522, line number 1777, construction number 34322.
Hope that gives some insight