@misc{indiciaef7c7627edd2d,
  title = {Multiplicative Systems: I.},
  author = {C J Everett and S Ulam},
  year = {1948},
  doi = {10.1073/pnas.34.8.403},
  url = {https://pubmed.ncbi.nlm.nih.gov/16588820/},
  note = {Source identifier: 16588820}
}