qmk_firmware/keyboards/handwired/twentypad/keymaps/default/keymap.json

{
    "keyboard": "handwired/twentypad",
    "keymap": "default",
    "layout": "LAYOUT_ortho_5x4",
    "layers": [
        [
            "KC_CALCULATOR", "KC_KP_SLASH", "KC_KP_ASTERISK", "KC_KP_MINUS",
            "KC_KP_7", "KC_KP_8", "KC_KP_9", "KC_KP_PLUS",
            "KC_KP_4", "KC_KP_5", "KC_KP_6", "KC_LEFT_PAREN",
            "KC_KP_1", "KC_KP_2", "KC_KP_3", "KC_RIGHT_PAREN",
            "KC_KP_0", "KC_KP_DOT", "KC_KP_EQUAL", "KC_KP_ENTER"
        ]
    ]
}