Thanks everyone, I'll remember to check pattern collections before posting next time.

mniemiec wrote:but the pattern file in my collection is dated 2000-04-14, so the synthesis is at least that old. It has three syntheses, from 24, 28, and 34 gliders respectively.

18, assuming the block+blinker takes 4 gliders:

`x = 108, y = 38, rule = Life`

4bo$2bobo$3b2o73bo$79bo$77b3o$21bo$21bo$21bo65b2o$14bo67bo4b2o$12bobo

66bobo$13b2o67bo$24b2o$24b2o2$88bo$47bo40b2o$15b3o28bo40bo2bo4bo$17bo

28b3o38bobo3bo2bo$16bo69bo2bo3bobo$32bo54bo4bo2bo$3o28bo61b2o$2bo28b3o

60bo$bo3$23b2o75bo$23b2o74bobo$34b2o58b2o4bo$34bobo57b2o$34bo$27bo$27b

o$27bo$105b3o$105bo$44b2o60bo$44bobo$44bo!

Edit: This reaction looks cheaper to synthesise, but I have no idea how to create the spark + glider:

`x = 59, y = 28, rule = B3/S23`

3b2o$3b3o9bo10bo$bob3o10bo7b2o$12b6o$3bo12bo9bobo$bob3o9bo11b2o$o26bo

16bo$bob3o36b2o2$44bobo$39bo5b2o$39bo5bo$38bobo$39bo$39bo5$57bo$57bo$

56bobo$51bo5bo$50b2o5bo$50bobo2$53b2o$52bo!

Edit2: Syntheses of a few miscellaneous objects:

`x = 218, y = 97, rule = Life`

78bo$79bo$77b3o$14bo$13bo$4bo8b3o$5b2o$4b2o4$84bobo$bo83b2o$2bo82bo$3o

15b2o$17bobo91bo$19bo2bo88bobo$3b2o17bobo61bobo22b2o$2bobo17b2o63b2o$

4bo82bo$21bo$21b2o84bo$20bobo83bo$106b3o3$99bo$97bobo9bobo$98b2o9b2o$

110bo2$106bo$107bo$105b3o$110bo$109bo$109b3o6$103b3o$103bo$104bo$100b

3o$102bo$101bo7$33bo$21bobo7b2o$22b2o8b2o4bo$22bo14bo$37b3o$16bo$17b2o

$16b2o5$146bo$107bo9bo18b2o8bobo56bo$108bo7bo18bo2bo7b2o23b2o30bobo9b

2o$16bo9b3o77b3o7b3o17bobo31bo2bo30b2o8bo2bo$16b2o10bo82b2o24bo33bobo

33b2ob2o2bob2o$15bobo9bo83bobo26b3o3b3o23bo3bo30b2obobobo$111bo34bo29b

o35bobo$119b2o26bo28bo35bob2o$119bobo57b2o32bo$119bo58bo2bo32bobo$179b

obo33b2o$33b2o113b2o30bo$32b2o114bobo52b2o$34bo113bo54bobo$204b2o$19b

2o$20b2o181bo$19bo182b2o$160b3o39bobo$162bo19b2o$161bo20bobo$182bo4$

62b3o$62bo$63bo$10b2o$11b2o$10bo!

And possible reductions to Octagon 4 and Jack::

`x = 22, y = 22, rule = Life`

14bo$13bobo$6bo6bobo$6bobo5bo$6bobo$7b2o$b2o14b3o$o2bo12bo$b2o13b3o5$

3b3o13b2o$5bo12bo2bo$2b3o14b2o$13b2o$13bobo$7bo5bobo$6bobo6bo$6bobo$7b

o!

`x = 17, y = 21, rule = B3/S23`

2bo11bo$2bo11bo$2b2o9b2o$4b2o5b2o$3b2o7b2o$3bo9bo3$2bo11bo$bobo9bobo$o

3bo7bo3bo$bobo9bobo$2bo11bo3$3bo9bo$3b2o7b2o$4b2o5b2o$2b2o9b2o$2bo11bo

$2bo11bo!

What programs are good for finding syntheses of these small, unstable patterns?