A257471 Sequence obtained from A003991 (multiplication table read by antidiagonals) by removing repetitions.

1, 2, 3, 4, 6, 5, 8, 9, 10, 12, 7, 15, 16, 14, 18, 20, 21, 24, 25, 28, 30, 11, 27, 32, 35, 36, 22, 40, 42, 13, 33, 45, 48, 49, 26, 44, 50, 54, 56, 39, 55, 60, 63, 64, 52, 66, 70, 72, 17, 65, 77, 80, 81, 34, 78, 84, 88, 90, 19, 51, 75, 91, 96, 99, 100

Offset: 1

Author

Ivan Neretin, Apr 25 2015

Keywords

• nonn
• easy
• look

Comments

A permutation of positive integers.

Examples

			The infinite multiplication table
1...2...3...4...5...
2...4...6...8..10...
3...6...9..12..15...
4...8..12..16..20...
5..10..15..20..25...
...
reads by antidiagonals as follows: 1, 2, 2, 3, 4, 3, 4, 6, 6, 4, 5, 8, 9, 8, 5, ... (A003991). By removing all numbers that were encountered previously, we get 1, 2, 3, 4, 6, 5, 8, 9, ...
		

Links

• Ivan Neretin, Table of n, a(n) for n = 1..10000
• Index entries for sequences that are permutations of the natural numbers

Crossrefs

Cf. A003991 (multiplication table), A257472 (inverse permutation).

Programs

Mathematica

DeleteDuplicates[Flatten[Table[i * (n - i), {n, 20}, {i, n - 1}]]]