IMHO the best option would be to connect them in series strings, add a resistor to limit the current and run them from a higher voltage. Eight strings of three, (yes you'll have one left over) each consisting of three LEDs with the two wires to the middle LED each soldered to ONE wire of the OTHER colour of the end LEDs. That will give a string that takes 20mA max and has a bit under 9V across it when running. If you want a lot of brightness, add a 270 ohm resistor (solder it to the free red wire of the end LED) and you'll have a string that will be quite happy running from a 12V Lead Acid battery, as long as the battery isn't connected to a fast charger or a running vehicle. A float (trickle) charger would be OK. The strings would connect in parallel - free lead wires of all the resistors together, then via a 1A fuse to the battery positive (and also via a switch if you want one), all free black wires togethyer and to the battery negative. You can use as much flex as you need between the joined LED string connections and the battery - cheap thin flat twin cable (aka 'bell wire' - get the stuff with a stripe down one wire so you don't get them mixed up), will do nicely. Put the fuse at the battery end.
Over 10 days, running 24/7 they'll need a bit under 35AH. If you want a lead acid leasure battery to survive in cyclic use, you don't discharge it past 40%, and it may be difficult to get it above 90% charge on a cheap charger so only 50% of the nameplate rating is really usable. Therefore the minimum battery capacity would be 70AH. A 60AH battery would be discharged to 35%, which is pushing it a bit but would be OK for a one-off. A >100AH car battery from a scrapyard would probably also do, but you can never be sure how much capacity a scrapyard battery's got left. Charge the battery beforehand taking it off-charge no more than a couple of days in advance, and if you want the battery to survive, get it back on charge within a day of the end of the display. DO NOT leave it running till the battery is flat - I figured for 10 days, if you go over that the odds of killing the battery stone dead go up steeply with each extra day.
For the odd one out, if you *MUST* use it, use a 720 ohm resistor then treat it like one of the three LED strings. It will start off a bit dimmer with a fully charged battery and end up a bit brighter. Alternatively you could do two strings of two, with 470 ohm resistors. Again the brightness wont match, but four slightly different may be easier to distribute artistically than one.
N.B. you cant switch individual LEDs On/Off - you could however switch any string as a whole.
If you want lower brightness, try using higher value resistors - I wouldn't advise going lower for brighter as there is a big risk of blowing the LEDs.
If in doubt *ASK*!