So I noticed this meme going around (https://imgur.com/Gl8omZb) and wanted to see which pokemon were unreachable with the algorithm they present. Turns out there are a lot. Depends upon the pykemon library.
Full list of Pokemon that are impossible to get: Unfezant, Roggenrola, Excadrill, Gurdurr, Klinklang, Scolipede, Lilligant, Whimsicott, Vulpix, Zubat, Oddish, Dwebble, Parasect, Tirtouga, Persian, Archen, Arcanine, Poliwhirl, Machoke, Vanillite, Victreebel, Tentacruel, Geodude, Slowpoke, Frillish, Magneton, Farfetchd, Ferroseed, Seel, Klink, Muk, Tynamo, Gengar, Cubchoo, Hypno, Axew, Fraxure, Electrode, Exeggutor, Hitmonlee, Hitmonchan, Koffing, Golett, Rhyhorn, Chansey, Bouffalant, Braviary, Vullaby, Goldeen, Deino, Mr-mime, Scyther, Larvesta, Pinsir, Magikarp, Thundurus-incarnate, Lapras, Landorus-incarnate, Vaporeon, Keldeo-ordinary, Porygon, Omastar, Kabutops, Aerodactyl, Moltres, Dragonair, Dragonite, Mew, Typhlosion, Totodile, Croconaw, Hoothoot, Noctowl, Ledian, Spinarak, Pichu, Cleffa, Natu, Xatu, Mareep, Ampharos, Marill, Sudowoodo, Skiploom, Sunkern, Yanma, Wooper, Umbreon, Slowking, Unown, Wobbuffet, Forretress, Dunsparce, Qwilfish, Scizor, Shuckle, Heracross, Sneasel, Cryogonal, Slugma, Magcargo, Corsola, Remoraid, Mantine, Skarmory, Houndoom, Terrakion, Porygon2, Smeargle, Tyrogue, Hitmontop, Elekid, Miltank, Entei, Larvitar, Krookodile, Lugia, Celebi, Sceptile, Blaziken, Mudkip, Marshtomp, Mightyena, Zigzagoon, Wurmple, Beautifly, Cascoon, Dustox, Lombre, Nuzleaf, Swellow, Wingull, Kirlia, Gardevoir, Surskit, Masquerain, Slakoth, Ninjask, Shedinja, Whismur, Exploud, Makuhita, Azurill, Delcatty, Sableye, Mawile, Lairon, Meditite, Electrike, Plusle, Volbeat, Illumise, Gulpin, Swalot, Carvanha, Wailord, Zangoose, Shuppet, Zoroark, Metagross, Latios, Groudon, Reuniclus, Scraggy, Pachirisu, Floatzel, Lopunny, Honchkrow, Bronzor, Gible, Riolu, Drapion, Toxicroak, Lumineon, Lickilicky, Electivire, Yanmega, Rotom, Heatran, Shaymin-land, Pignite, Dewott, Stoutland, Purrloin