Decimal sequences for cryptography. A recurring decimal such as 1/7=.142857142857... can be considered a periodic series with the digits 142857 in the base 10. In general, such sequences may be written to any base. The maximum period of such a d-sequence (when the base is not necessarily 10) written for 1/q, q prime, is q-1. A binary d-sequence may be written as: :a<sub>i</sub> = 2 mod q mod 2 As example, the d-sequence for 1/19 is 000011010111100101. S. Kak has proposed their use for error correction coding, cryptography and as random sequences. These sequences have fairly good autocorrelation properties.