Number 13

[ExTREm-San]

23 and 26 is the most anime series that I've watched.

[bitwar]

Typically, as has been said, you see mostly 26 episode series for TV, some 13 for TV and longer anime, and a few 52s here and there (Gundam anyone?). And also as was pointed out, it goes along with the number of weeks in a year, not neccessarily because they particularly like the numbers. For OAVs I guess, they decide that it's half as long as a tv series, since they're releases tend to be measured in months. Every once in a while, they'll put out a 49 episode series (Gundam Wing I think did this) or a 24 episode series (X-TV, if I remember correctly). OAVs, also see 6 episodes (BASTARD!, Iria). Actually, OAVs are kind of unpredictable as far as number of episodes go. Also, the "endless" series length seems to be making a comeback after an apparent absence for a while. At least in terms of the number of long running series. Or maybe I'm just imagining that because they seem so popular. . . Whatever.

[Death BOO Z]

in chirtianity, 13 is a number of bad luck, so i guess the jappanease use it to set off the mood, like how kenshin left to Kyoto at the 13th (i think it was the 13th, could be 14th)... robert jordan did the same at his wheel of time books, they use the number 13 a shitload of times...