OFFSET
1,3
LINKS
Peter Kagey, Table of n, a(n) for n = 1..10000
EXAMPLE
A000027 read by antidiagonals is:
1 2 4 7
3 5 8
6 9
...
Thus:
Row 1: []
Row 2: [1]
Row 3: [1, 2]
Row 4: [1, 2]
Row 5: [1, 2, 3, 4]
Row 6: [1, 3, 4, 5]
Row 7: [1, 2, 4]
Row 8: [2, 3, 4, 5, 7]
Row 9: [2, 3, 5, 6, 7, 8]
MATHEMATICA
nn = 18; t = Table[(n^2 - n)/2 + Accumulate@ Range[n - 1, Ceiling[(Sqrt[9 + 8 nn] - 3)/2]] + 1, {n, Ceiling[(Sqrt[9 + 8 nn] - 3)/2] + 1}]; Table[Function[a, Function[p, Most@ Union@ Flatten@ {Map[a[[#1, #2]] & @@ # &, Most@ NestWhileList[# - 1 &, First@ p, ! MemberQ[#, 0] &]], Range[SelectFirst[Reverse@ Join[{0}, First@ t], n >= # &], n - 1], Transpose[a][[ p[[1, 2]] ]], a[[ p[[1, 1]] ]]}]@ Position[a, n]]@ Array[t[[#1, #2]] &, First@ Position[t, n]], {n, nn}] // Flatten (* Michael De Vlieger, Jun 29 2016, Version 10 *)
PROG
(Haskell)
import Data.List (sort, nub)
a274080 n = a274080_list !! (n - 1)
a274080_list = concatMap a274080_row [1..]
a274080_tabf = map a274080_row [1..]
a274080_row n = nub $ sort $ concatMap (\f -> f n) [a274079_row, a273825_row, a273824_row, a273823_row]
CROSSREFS
KEYWORD
AUTHOR
Peter Kagey, Jun 09 2016
STATUS
approved