Mian–Chowla sequence
In mathematics, the Mian–Chowla sequence is an integer sequence defined recursively in the following way. The sequence starts with
Then for , is the smallest integer such that every pairwise sum
is distinct, for all and less than or equal to .
Properties
Initially, with , there is only one pairwise sum, 1 + 1 = 2. The next term in the sequence, , is 2 since the pairwise sums then are 2, 3 and 4, i.e., they are distinct. Then, can't be 3 because there would be the non-distinct pairwise sums 1 + 3 = 2 + 2 = 4. We find then that , with the pairwise sums being 2, 3, 4, 5, 6 and 8. The sequence thus begins
Similar sequences
If we define , the resulting sequence is the same except each term is one less (that is, 0, 1, 3, 7, 12, 20, 30, 44, 65, 80, 96, ... OEIS: A025582).
History
The sequence was invented by Abdul Majid Mian and Sarvadaman Chowla.
References
- S. R. Finch, Mathematical Constants, Cambridge (2003): Section 2.20.2
- R. K. Guy Unsolved Problems in Number Theory, New York: Springer (2003)