I've used a number of AVR chips. ATTiny85 is the smallest at 8 pins, ATTiny84 at 14 pins, ATTiny1634 at 20 pins, ATMega at 28 pins, and lastly ATMega1284 at 40 pins. Is there any AVR that can be used in Arduino IDE that fits between the last 2 and comes in DIP for breadboarding?
Beyond 1284, AVR only came in TQFP and are not breadboard friendly; ever try to insert or remove a 100 pin package? If you made a board adapter and managed to insert it in breadboard without breaking it, it'll probably never come back out. I asked already.
So you're only asking about pin count, correct?
2561, 64 pins.
I offer a board that’s a system on a chip, the crsystal and other parts are on the bottom.
Well, there's the 644 - the smaller-flash version of 1284p (also way less ram)
I wouldn't expect anything between the x8 series with 23 programmable io lines and the x4 series with 32 - I don't think there are even any common sizes of dip package between those...
" If you made a board adapter and managed to insert it in breadboard without breaking it, it’ll probably never come back out."
I also offer 2560 system on a board in DIP format