Thirteensome

Their search through the musical archives of our folk literature has brought to light a “Hawaiian Serf Surf Song,” which they are arranging for a “thirteensome” made up of eleven ukuleles, one mixed voice and a snare drum.

Source: wiktionary

Sometimes Jim and I would play golf together as part of a thirteensome. Jim would get about 13 guys together, all hitting balls on the same hole at the same time.

Source: wiktionary

So if you have an eightsome, it should be five girls and three guys. A thirteensome should be eight girls and five guys.

Source: wiktionary

And watch as Loki tried his damnednest to orchestrate a threesome, foursome, possibly thirteensome with his so-called supermodel cunt, and his several cunts amongst the Kensington girls, and maybe, if I'm smart, get a little action myself, from that girl from outside the coffee shop and from the streetcar and[…]

Source: wiktionary